docs/language/informal/implicit-creation.md - sdk.git - Git at Google

 # Implicit Creation

 Author: eernst@.

 Version: 0.7 (2018-04-10)

 Status: Background material, normative language now in dartLangSpec.tex.

 **This document** is an informal specification of the *implicit creation*
 feature. **The feature** adds support for omitting some occurrences of the
 reserved words `new` and `const` in instance creation expressions.

 This feature specification was written with a
 [combined proposal](https://github.com/dart-lang/sdk/blob/master/docs/language/informal/optional-new-const.md)
 as the starting point. That proposal presents optional new and optional const
 together with several other features.


 ## Motivation

 In Dart without implicit creation, the reserved word `new` is present in
 almost all expressions whose evaluation invokes a constructor at run time,
 and `const` is present in the corresponding constant expressions. These
 expressions are known as *instance creation expressions*. If `new` or
 `const` is removed from such an instance creation expression, the remaining
 phrase is still syntactically correct in most cases. This feature
 specification updates the grammar to make them all syntactically correct.

 With that grammar update, all instance creation expressions can technically
 omit `new` or `const` because tools (compilers, analyzers) are able to
 parse these expressions.  The tools are able to recognize that these
 expressions denote instance creations (rather than, say, static function
 invocations), because the part before the arguments is statically known to
 denote a constructor.

 For instance, `p.C.foo` may resolve statically to a constructor named `foo` in
 a class `C` imported with prefix `p`. Similarly, `D` may resolve to a class, in
 which case `D(42)` is statically known to be a constructor invocation because
 the other interpretation is statically known to be incorrect (that is, cf.
 section '16.14.3 Unqualified Invocation' in the language specification,
 evaluating `(D)(42)`: `(D)` is an instance of `Type` which is not a function
 type and does not have a method named `call`, so we cannot call `(D)`).

 In short, even without the keyword, we can still unambiguously recognize the
 expressions that create objects. In that sense, the keywords are superfluous.

 For human readers, however, it may be helpful to document that a particular
 expression will yield a fresh instance, and this is the most common argument why
 `new` should *not* be omitted: It can be good documentation. But Dart already
 allows instance creation expressions to invoke a factory constructor, which is
 not guaranteed to return a newly created object, so Dart developers never had
 any firm local guarantees that any particular expression would yield a fresh
 object. This means that it may very well be justified to have an explicit `new`,
 but it will never be a rigorous guarantee of freshness.

 Similarly, it may be important for developers to ensure that certain expressions
 are constant, because of the improved performance and the guaranteed
 canonicalization. This is a compelling argument in favor of making certain
 instance creation expressions constant: It is simply a bug for that same
 expression to have `new` because object identity is an observable
 characteristic, and it may be crucial for performance that the expression is
 constant.

 In summary, both `new` and `const` may always be omitted from an instance
 creation expression, but it is useful and reasonable to allow an explicit `new`,
 and it is necessary to allow an explicit `const`. Based on that line of
 reasoning, we've decided to make them optional. It will then be possible for
 developers to make many expressions considerably more concise, and they can
 still enforce the desired semantics as needed.

 Obviously, this underscores the importance of the default: When a given
 instance creation expression omits the keyword, should it be `const` or
 `new`?

 **As a general rule** `const` is used whenever it is required, and
 otherwise `new` is used. This requirement arises from the syntactic
 context, based on the fact that a non-constant expression would be a
 compile-time error.

 In summary, the implicit creation feature allows for concise construction
 of objects, and it still allows developers to explicitly specify `new` or
 `const`, whenever needed and whenever it is considered to be good
 documentation.


 ## Syntax

 The syntax changes associated with this feature are the following:

 ```
 postfixExpression ::=
     assignableExpression postfixOperator |
     constructorInvocation selector* |  // NEW
     primary selector*
 constructorInvocation ::=  // NEW
     typeName typeArguments '.' identifier arguments
 assignableExpression ::=
     SUPER unconditionalAssignableSelector |
     constructorInvocation assignableSelectorPart+ |  // NEW
     identifier |
     primary assignableSelectorPart+
 assignableSelectorPart ::=
     argumentPart* assignableSelector
 ```


 ## Static analysis

 We specify a type directed source code transformation which eliminates the
 feature by expressing the same semantics with different syntax. The static
 analysis proceeds to work on the transformed program.

 *This means that the feature is "static semantic sugar". We do not specify the
 dynamic semantics for this feature, because the feature is eliminated in this
 transformation step.*

 We need to treat expressions differently in different locations, hence the
 following definition: An expression _e_ is said to *occur in a constant
 context*,

 - if _e_ is an element of a constant list literal, or a key or value of
   an entry of a constant map literal.
 - if _e_ is an actual argument of a constant object expression or of a
   metadata annotation.
 - if _e_ is the initializing expression of a constant variable declaration.
 - if _e_ is a switch case expression.
 - if _e_ is an immediate subexpression of an expression _e1_ which occurs in
   a constant context, unless _e1_ is a `throw` expression or a function
   literal.

 *This roughly means that everything which is inside a syntactically
 constant expression or declaration is in a constant context. Note that a
 `const` modifier which is introduced by the source code transformation does
 not create a constant context, it is only the explicit occurrences of
 `const` in the program that create a constant context. Also note that a
 `throw` expression is currently not allowed in a constant expression, but
 extensions affecting that status may be considered. A similar situation
 arises for function literals.*

 *A formal parameter may have a default value, which must be a constant
 expression. We have chosen to not put such default values into a constant
 context. They must be constant, and it may be necessary to add the keyword
 `const` in order to make them so. This may seem inconvenient at times, but
 the rationale is that it allows for future generalizations of default value
 expressions allowing them to be non-constant. Still, there is no guarantee
 that such features will be added to Dart.*

 *For a class which contains a constant constructor and an instance variable
 which is initialized by an expression _e_, it is a compile-time error if
 _e_ is not constant. We have chosen to not put such initializers into a
 constant context, and hence an explicit `const` may be required. This may
 again seem inconvenient at times, but the rationale is that the reason for
 the constancy requirement is non-local (the constant constructor
 declaration may be many lines away from the instance variable declaration);
 it may break programs in surprising and confusing ways if a constructor is
 changed to be constant; and it may cause subtle bugs at run time due to the
 change in identity, if such a change is made and it does not cause any
 compile-time errors.*

 We define *new/const insertion* as the following transformation, which will
 be applied to specific parts of the program as specified below:

 - if the expression _e_ occurs in a constant context, replace _e_ by
   `const` _e_,
 - otherwise replace _e_ by `new` _e_.

 *Note that new/const insertion is just a syntactic transformation, it is
 specified below where to apply it, including which syntactic constructs may
 play the role of _e_.*

 *Also note that the outcome of new/const insertion may have static semantic
 errors, e.g., actual arguments to a constructor invocation may have wrong
 types because that's how the program was written, or a `const` list may
 have elements which are not constant expressions. In such cases, tools like
 analyzers and compilers should emit diagnostic messages that are meaningful
 in relation to the original source of the program, which might mean that
 the blame is assigned to a larger syntactic construct than the one that
 directly has a compile-time error after the transformation.*

 *We specify the transformation as based on a depth-first traversal of an
 abstract syntax tree (AST). This means that the program is assumed to be
 free of syntax errors, and when the current AST is, e.g., a
 `postfixExpression`, the program as a whole has such a structure that the
 current location was parsed as a `postfixExpression`. This is different
 from the situation where we just require that a given subsequence of the
 tokens of the program allows for such a parsing in isolation. For instance,
 an identifier like `x` parses as an `assignableExpression` in isolation,
 but if it occurs in the context `var x = 42;` or `var y = x;` then it will
 not be parsed as an `assignableExpression`, it will be parsed as a plain
 `identifier` which is part of a `declaredIdentifier` in the first case, and
 as a `primary` which is a `postfixExpression`, which is a
 `unaryExpression`, etc., in the second case. In short, we are transforming
 the AST of the program as a whole, not isolated snippets of code.*

 *In scientific literature, this kind of transformation is commonly
 specified as an inductive transformation where `[[e1 e2]] = [[e1]] [[e2]]`
 when the language supports a construct of the form `e1 e2`, etc. The reader
 may prefer to view the transformation in that light, and we would then say
 that we have omitted all the congruence rules.*

 For the purposes of describing the transformation on assignable expressions
 we need the following syntactic entity:

 ```
 assignableExpressionTail ::=
     arguments assignableSelector assignableSelectorPart*
 ```

 The transformation proceeds as follows, with three groups of situations
 where a transformation is applied:

 1.  With a `postfixExpression` _e_,

     - if _e_ is of the form `constructorInvocation selector*`, i.e.,
       `typeName typeArguments '.' identifier arguments selector*` then
       perform new/const insertion on the initial `constructorInvocation`.
     - if _e_ is of the form `typeIdentifier arguments` where
       `typeIdentifier` denotes a class then perform new/const insertion on
       _e_.
     - if _e_ is of the form `identifier1 '.' identifier2 arguments` where
       `identifier1` denotes a class and `identifier2` is the name of a
       named constructor in that class, or `identifier1` denotes a prefix
       for a library _L_ and `identifier2` denotes a class exported by _L_,
       perform new/const insertion on _e_.
     - if _e_ is of the form
       `identifier1 '.' typeIdentifier '.' identifier2 arguments`
       where `identifier1` denotes a library prefix for a library _L_,
       `typeIdentifier` denotes a class _C_ exported by _L_, and
       `identifier2` is the name of a named constructor in _C_, perform
       new/const insertion on _e_.

 2.  With an `assignableExpression` _e_,

     - if _e_ is of the form
       `constructorInvocation assignableSelectorPart+`
       then perform new/const insertion on the initial
       `constructorInvocation`.
     - if _e_ is of the form `typeIdentifier assignableExpressionTail` where
       `typeIdentifier` denotes a class then perform new/const insertion on
       the initial `typeIdentifier arguments`.
     - if _e_ is of the form
       `typeIdentifier '.' identifier assignableExpressionTail`
       where `typeIdentifier` denotes a class and `identifier` is the name
       of a named constructor in that class, or `typeIdentifier` denotes a
       prefix for a library _L_ and `identifier` denotes a class exported by
       _L_ then perform new/const insertion on the initial
       `typeIdentifier '.' identifier arguments`.
     - if _e_ is of the form
       `typeIdentifier1 '.' typeIdentifier2 '.' identifier
       assignableExpressionTail`
       where `typeIdentifier1` denotes a library prefix for a library _L_,
       `typeIdentifier2` denotes a class _C_ exported by _L_, and
       `identifier` is the name of a named constructor in _C_ then perform
       new/const insertion on the initial
       `typeIdentifier1 '.' typeIdentifier2 '.' identifier arguments`.

 3.  If _e_ is a literal list or a literal map which occurs in a constant
     context and does not have the modifier `const`, it is replaced by
     `const` _e_.

 *In short, `const` is added implicitly in almost all situations where it is
 required by the context, and in other situations `new` is added on instance
 creations. It is easy to verify that each of the replacements can be
 derived from `postfixExpression` via `primary selector*` and similarly for
 `assignableExpression`. Hence, the transformation preserves syntactic
 correctness.*


 ## Dynamic Semantics

 There is no dynamic semantics to specify for this feature, because it is
 eliminated by the code transformation.


 ## Revisions

 - 0.7 (2018-04-10) Clarified the structure of the algorithm. Added
   commentary about cases where there is no constant context even though a
   constant expression is required, with a motivation for why it is so.

 - 0.6 (2018-04-06) Removed "magic const" again, due to the risks
   associated with this feature (getting it specified and implemented
   robustly, in time).

 - 0.5 (2018-01-04) Rewritten to use `const` whenever possible (aka "magic
   const") and adjusted to specify optional const as well as optional new
   together, because they are now very closely connected. This document was
   renamed to 'implicit-creation.md', and the document 'optional-const.md'
   was deleted.

 - 0.4 (2017-10-17) Reverted to use 'immediate subexpression' again, for
   correctness. Adjusted terminology for consistency. Clarified the semantics
   of the transformation.

 - 0.3 (2017-09-08) Included missing rule for transformation of composite
   literals (lists and maps). Eliminated the notion of an immediate
   subexpression, for improved precision.

 - 0.2 (2017-07-30) Updated the document to specify the previously missing
   transformations for `assignableExpression`, and to specify a no-magic
   approach (where no `const` is introduced except when forced by the
   syntactic context).

 - 0.1 (2017-08-15) Stand-alone informal specification for optional new created,
   using version 0.8 of the combined proposal
   [optional-new-const.md](https://github.com/dart-lang/sdk/blob/master/docs/language/informal/optional-new-const.md)
   as the starting point.
	# Implicit Creation

	Author: eernst@.

	Version: 0.7 (2018-04-10)

	Status: Background material, normative language now in dartLangSpec.tex.

	This document is an informal specification of the implicit creation
	feature. The feature adds support for omitting some occurrences of the
	reserved words `new` and `const` in instance creation expressions.

	This feature specification was written with a
	[combined proposal](https://github.com/dart-lang/sdk/blob/master/docs/language/informal/optional-new-const.md)
	as the starting point. That proposal presents optional new and optional const
	together with several other features.


	## Motivation

	In Dart without implicit creation, the reserved word `new` is present in
	almost all expressions whose evaluation invokes a constructor at run time,
	and `const` is present in the corresponding constant expressions. These
	expressions are known as instance creation expressions. If `new` or
	`const` is removed from such an instance creation expression, the remaining
	phrase is still syntactically correct in most cases. This feature
	specification updates the grammar to make them all syntactically correct.

	With that grammar update, all instance creation expressions can technically
	omit `new` or `const` because tools (compilers, analyzers) are able to
	parse these expressions. The tools are able to recognize that these
	expressions denote instance creations (rather than, say, static function
	invocations), because the part before the arguments is statically known to
	denote a constructor.

	For instance, `p.C.foo` may resolve statically to a constructor named `foo` in
	a class `C` imported with prefix `p`. Similarly, `D` may resolve to a class, in
	which case `D(42)` is statically known to be a constructor invocation because
	the other interpretation is statically known to be incorrect (that is, cf.
	section '16.14.3 Unqualified Invocation' in the language specification,
	evaluating `(D)(42)`: `(D)` is an instance of `Type` which is not a function
	type and does not have a method named `call`, so we cannot call `(D)`).

	In short, even without the keyword, we can still unambiguously recognize the
	expressions that create objects. In that sense, the keywords are superfluous.

	For human readers, however, it may be helpful to document that a particular
	expression will yield a fresh instance, and this is the most common argument why
	`new` should not be omitted: It can be good documentation. But Dart already
	allows instance creation expressions to invoke a factory constructor, which is
	not guaranteed to return a newly created object, so Dart developers never had
	any firm local guarantees that any particular expression would yield a fresh
	object. This means that it may very well be justified to have an explicit `new`,
	but it will never be a rigorous guarantee of freshness.

	Similarly, it may be important for developers to ensure that certain expressions
	are constant, because of the improved performance and the guaranteed
	canonicalization. This is a compelling argument in favor of making certain
	instance creation expressions constant: It is simply a bug for that same
	expression to have `new` because object identity is an observable
	characteristic, and it may be crucial for performance that the expression is
	constant.

	In summary, both `new` and `const` may always be omitted from an instance
	creation expression, but it is useful and reasonable to allow an explicit `new`,
	and it is necessary to allow an explicit `const`. Based on that line of
	reasoning, we've decided to make them optional. It will then be possible for
	developers to make many expressions considerably more concise, and they can
	still enforce the desired semantics as needed.

	Obviously, this underscores the importance of the default: When a given
	instance creation expression omits the keyword, should it be `const` or
	`new`?

	As a general rule `const` is used whenever it is required, and
	otherwise `new` is used. This requirement arises from the syntactic
	context, based on the fact that a non-constant expression would be a
	compile-time error.

	In summary, the implicit creation feature allows for concise construction
	of objects, and it still allows developers to explicitly specify `new` or
	`const`, whenever needed and whenever it is considered to be good
	documentation.


	## Syntax

	The syntax changes associated with this feature are the following:

	```
	postfixExpression ::=
	assignableExpression postfixOperator \|
	constructorInvocation selector* \| // NEW
	primary selector*
	constructorInvocation ::= // NEW
	typeName typeArguments '.' identifier arguments
	assignableExpression ::=
	SUPER unconditionalAssignableSelector \|
	constructorInvocation assignableSelectorPart+ \| // NEW
	identifier \|
	primary assignableSelectorPart+
	assignableSelectorPart ::=
	argumentPart* assignableSelector
	```


	## Static analysis

	We specify a type directed source code transformation which eliminates the
	feature by expressing the same semantics with different syntax. The static
	analysis proceeds to work on the transformed program.

	*This means that the feature is "static semantic sugar". We do not specify the
	dynamic semantics for this feature, because the feature is eliminated in this
	transformation step.*

	We need to treat expressions differently in different locations, hence the
	following definition: An expression _e_ is said to *occur in a constant
	context*,

	- if _e_ is an element of a constant list literal, or a key or value of
	an entry of a constant map literal.
	- if _e_ is an actual argument of a constant object expression or of a
	metadata annotation.
	- if _e_ is the initializing expression of a constant variable declaration.
	- if _e_ is a switch case expression.
	- if _e_ is an immediate subexpression of an expression _e1_ which occurs in
	a constant context, unless _e1_ is a `throw` expression or a function
	literal.

	*This roughly means that everything which is inside a syntactically
	constant expression or declaration is in a constant context. Note that a
	`const` modifier which is introduced by the source code transformation does
	not create a constant context, it is only the explicit occurrences of
	`const` in the program that create a constant context. Also note that a
	`throw` expression is currently not allowed in a constant expression, but
	extensions affecting that status may be considered. A similar situation
	arises for function literals.*

	*A formal parameter may have a default value, which must be a constant
	expression. We have chosen to not put such default values into a constant
	context. They must be constant, and it may be necessary to add the keyword
	`const` in order to make them so. This may seem inconvenient at times, but
	the rationale is that it allows for future generalizations of default value
	expressions allowing them to be non-constant. Still, there is no guarantee
	that such features will be added to Dart.*

	*For a class which contains a constant constructor and an instance variable
	which is initialized by an expression _e_, it is a compile-time error if
	_e_ is not constant. We have chosen to not put such initializers into a
	constant context, and hence an explicit `const` may be required. This may
	again seem inconvenient at times, but the rationale is that the reason for
	the constancy requirement is non-local (the constant constructor
	declaration may be many lines away from the instance variable declaration);
	it may break programs in surprising and confusing ways if a constructor is
	changed to be constant; and it may cause subtle bugs at run time due to the
	change in identity, if such a change is made and it does not cause any
	compile-time errors.*

	We define new/const insertion as the following transformation, which will
	be applied to specific parts of the program as specified below:

	- if the expression _e_ occurs in a constant context, replace _e_ by
	`const` _e_,
	- otherwise replace _e_ by `new` _e_.

	*Note that new/const insertion is just a syntactic transformation, it is
	specified below where to apply it, including which syntactic constructs may
	play the role of _e_.*

	*Also note that the outcome of new/const insertion may have static semantic
	errors, e.g., actual arguments to a constructor invocation may have wrong
	types because that's how the program was written, or a `const` list may
	have elements which are not constant expressions. In such cases, tools like
	analyzers and compilers should emit diagnostic messages that are meaningful
	in relation to the original source of the program, which might mean that
	the blame is assigned to a larger syntactic construct than the one that
	directly has a compile-time error after the transformation.*

	*We specify the transformation as based on a depth-first traversal of an
	abstract syntax tree (AST). This means that the program is assumed to be
	free of syntax errors, and when the current AST is, e.g., a
	`postfixExpression`, the program as a whole has such a structure that the
	current location was parsed as a `postfixExpression`. This is different
	from the situation where we just require that a given subsequence of the
	tokens of the program allows for such a parsing in isolation. For instance,
	an identifier like `x` parses as an `assignableExpression` in isolation,
	but if it occurs in the context `var x = 42;` or `var y = x;` then it will
	not be parsed as an `assignableExpression`, it will be parsed as a plain
	`identifier` which is part of a `declaredIdentifier` in the first case, and
	as a `primary` which is a `postfixExpression`, which is a
	`unaryExpression`, etc., in the second case. In short, we are transforming
	the AST of the program as a whole, not isolated snippets of code.*

	*In scientific literature, this kind of transformation is commonly
	specified as an inductive transformation where `[[e1 e2]] = [[e1]] [[e2]]`
	when the language supports a construct of the form `e1 e2`, etc. The reader
	may prefer to view the transformation in that light, and we would then say
	that we have omitted all the congruence rules.*

	For the purposes of describing the transformation on assignable expressions
	we need the following syntactic entity:

	```
	assignableExpressionTail ::=
	arguments assignableSelector assignableSelectorPart*
	```

	The transformation proceeds as follows, with three groups of situations
	where a transformation is applied:

	1. With a `postfixExpression` _e_,

	- if _e_ is of the form `constructorInvocation selector*`, i.e.,
	`typeName typeArguments '.' identifier arguments selector*` then
	perform new/const insertion on the initial `constructorInvocation`.
	- if _e_ is of the form `typeIdentifier arguments` where
	`typeIdentifier` denotes a class then perform new/const insertion on
	_e_.
	- if _e_ is of the form `identifier1 '.' identifier2 arguments` where
	`identifier1` denotes a class and `identifier2` is the name of a
	named constructor in that class, or `identifier1` denotes a prefix
	for a library _L_ and `identifier2` denotes a class exported by _L_,
	perform new/const insertion on _e_.
	- if _e_ is of the form
	`identifier1 '.' typeIdentifier '.' identifier2 arguments`
	where `identifier1` denotes a library prefix for a library _L_,
	`typeIdentifier` denotes a class _C_ exported by _L_, and
	`identifier2` is the name of a named constructor in _C_, perform
	new/const insertion on _e_.

	2. With an `assignableExpression` _e_,

	- if _e_ is of the form
	`constructorInvocation assignableSelectorPart+`
	then perform new/const insertion on the initial
	`constructorInvocation`.
	- if _e_ is of the form `typeIdentifier assignableExpressionTail` where
	`typeIdentifier` denotes a class then perform new/const insertion on
	the initial `typeIdentifier arguments`.
	- if _e_ is of the form
	`typeIdentifier '.' identifier assignableExpressionTail`
	where `typeIdentifier` denotes a class and `identifier` is the name
	of a named constructor in that class, or `typeIdentifier` denotes a
	prefix for a library _L_ and `identifier` denotes a class exported by
	_L_ then perform new/const insertion on the initial
	`typeIdentifier '.' identifier arguments`.
	- if _e_ is of the form
	`typeIdentifier1 '.' typeIdentifier2 '.' identifier
	assignableExpressionTail`
	where `typeIdentifier1` denotes a library prefix for a library _L_,
	`typeIdentifier2` denotes a class _C_ exported by _L_, and
	`identifier` is the name of a named constructor in _C_ then perform
	new/const insertion on the initial
	`typeIdentifier1 '.' typeIdentifier2 '.' identifier arguments`.

	3. If _e_ is a literal list or a literal map which occurs in a constant
	context and does not have the modifier `const`, it is replaced by
	`const` _e_.

	*In short, `const` is added implicitly in almost all situations where it is
	required by the context, and in other situations `new` is added on instance
	creations. It is easy to verify that each of the replacements can be
	derived from `postfixExpression` via `primary selector*` and similarly for
	`assignableExpression`. Hence, the transformation preserves syntactic
	correctness.*


	## Dynamic Semantics

	There is no dynamic semantics to specify for this feature, because it is
	eliminated by the code transformation.


	## Revisions

	- 0.7 (2018-04-10) Clarified the structure of the algorithm. Added
	commentary about cases where there is no constant context even though a
	constant expression is required, with a motivation for why it is so.

	- 0.6 (2018-04-06) Removed "magic const" again, due to the risks
	associated with this feature (getting it specified and implemented
	robustly, in time).

	- 0.5 (2018-01-04) Rewritten to use `const` whenever possible (aka "magic
	const") and adjusted to specify optional const as well as optional new
	together, because they are now very closely connected. This document was
	renamed to 'implicit-creation.md', and the document 'optional-const.md'
	was deleted.

	- 0.4 (2017-10-17) Reverted to use 'immediate subexpression' again, for
	correctness. Adjusted terminology for consistency. Clarified the semantics
	of the transformation.

	- 0.3 (2017-09-08) Included missing rule for transformation of composite
	literals (lists and maps). Eliminated the notion of an immediate
	subexpression, for improved precision.

	- 0.2 (2017-07-30) Updated the document to specify the previously missing
	transformations for `assignableExpression`, and to specify a no-magic
	approach (where no `const` is introduced except when forced by the
	syntactic context).

	- 0.1 (2017-08-15) Stand-alone informal specification for optional new created,
	using version 0.8 of the combined proposal
	[optional-new-const.md](https://github.com/dart-lang/sdk/blob/master/docs/language/informal/optional-new-const.md)
	as the starting point.