std.meta

Templates to manipulate spec/template (also known as alias sequences).

Some operations on alias sequences are built into the language, such as S[i], which accesses the element at index i in the sequence. S[low .. high] returns a new alias sequence that is a slice of the old one.

For more information, see ctarguments, Compile-time Sequences, Compile-time Sequences.

Note

Several templates in this module use or operate on eponymous templates that

take a single argument and evaluate to a boolean constant. Such templates are referred to as template predicates.

Category Templates
Building blocks Alias

AliasSeq aliasSeqOf

Alias sequence filtering Erase

EraseAll Filter NoDuplicates Stride

Alias sequence type hierarchy DerivedToFront

MostDerived

Alias sequence transformation Repeat

Replace ReplaceAll Reverse staticMap staticSort

Alias sequence searching allSatisfy

anySatisfy staticIndexOf

Template predicates templateAnd

templateNot templateOr staticIsSorted

Template instantiation ApplyLeft

ApplyRight Instantiate

References: Based on ideas in Table 3.1 from Modern C++ Design, Andrei Alexandrescu (Addison-Wesley Professional, 2001)

Copyright

Copyright The D Language Foundation 2005 - 2015.

License

Boost License 1.0.

Authors

Walter Bright,

David Nadlinger Source: std/meta.d

tmpl aliasSeqOf AppendUnique ApplyLeft ApplyRight DerivedToFront Erase EraseAll Filter GenericReplace isLessEq isSame isSame MostDerived NoDuplicates OldAlias OldAlias Pack Repeat Replace Replace Replace Replace ReplaceAll Reverse SmartAlias staticIndexOf staticMap staticMerge staticSort Stride templateAnd templateNot templateOr
alias Alias Alias AliasSeq Instantiate

Types 4

aliasAliasSeq(TList...) = TList

Creates a sequence of zero or more aliases. This is most commonly used as template parameters or arguments.

In previous versions of Phobos, this was known as TypeTuple.

aliasAlias(alias a) = a

Allows aliasing of any single symbol, type or compile-time expression.

Not everything can be directly aliased. An alias cannot be declared of - for example - a literal: 

alias a = 4; //Error

With this template any single entity can be aliased: 

alias b = Alias!4; //OK

See Also

To alias more than one thing at once, use AliasSeq.
aliasAlias(T) = T

Ditto

aliasInstantiate(alias Template, Params...) = Template!Params

Instantiates the given template with the given parameters.

Used to work around syntactic limitations of D with regard to instantiating a template from an alias sequence (e.g. T[0]!(...) is not valid) or a template returning another template (e.g. Foo!(Bar)!(Baz) is not allowed).

Parameters

TemplateThe template to instantiate.
ParamsThe parameters with which to instantiate the template.

Returns

The instantiated template.

Templates 33

tmplOldAlias(alias a)
tmplOldAlias(T) if (!isAggregateType!T || is(Unqual!T == T))
tmplstaticIndexOf(args...) if (args.length >= 1)

Returns the index of the first occurrence of args[0] in the sequence args[1 .. $]. args may be types or compile-time values. If not found, -1 is returned.

tmplErase(args...) if (args.length >= 1)

Returns an AliasSeq created from args[1 .. $] with the first occurrence, if any, of args[0] removed.

tmplEraseAll(args...) if (args.length >= 1)

Returns an AliasSeq created from args[1 .. $] with all occurrences, if any, of args[0] removed.

tmplAppendUnique(items...)
tmplNoDuplicates(args...)

Returns an AliasSeq created from args with all duplicate types removed.

tmplReplace(T, U, TList...)

Returns an AliasSeq created from TList with the first occurrence of T, if found, replaced with U.

tmplReplace(alias T, U, TList...)

Ditto

tmplReplace(T, alias U, TList...)

Ditto

tmplReplace(alias T, alias U, TList...)

Ditto

tmplGenericReplace(args...) if (args.length >= 2)
tmplReplaceAll(args...)

Returns an AliasSeq created from args[2 .. $] with all occurrences of args[0], if any, replaced with args[1].

tmplReverse(args...)

Returns an AliasSeq created from args with the order reversed.

tmplMostDerived(T, TList...)

Returns the type from TList that is the most derived from type T. If no such type is found, T is returned.

tmplDerivedToFront(TList...)

Returns an AliasSeq with the elements of TList sorted so that the most derived types come first.

tmplstaticMap(alias fun, args...)

Evaluates to AliasSeq!(fun!(args[0]), fun!(args[1]), ..., fun!(args[$ - 1])).

tmplFilter(alias pred, args...)

Filters an AliasSeq using a template predicate. Returns an AliasSeq of the elements which satisfy the predicate.

tmpltemplateNot(alias pred)

Negates the passed template predicate.

tmpltemplateAnd(Preds...)

Combines several template predicates using logical AND, i.e. constructs a new predicate which evaluates to true for a given input T if and only if all of the passed predicates are true for T.

The predicates are evaluated from left to right, aborting evaluation in a short-cut manner if a false result is encountered, in which case the latter instantiations do not need to compile.

tmpltemplateOr(Preds...)

Combines several template predicates using logical OR, i.e. constructs a new predicate which evaluates to true for a given input T if and only at least one of the passed predicates is true for T.

The predicates are evaluated from left to right, aborting evaluation in a short-cut manner if a true result is encountered, in which case the latter instantiations do not need to compile.

tmplaliasSeqOf(alias iter) if (isIterable!(typeof(iter)) && !isInfinite!(typeof(iter)))

Converts any foreach-iterable entity (e.g. an input range) to an alias sequence.

Parameters

iterthe entity to convert into an AliasSeq. It must be able to be able to be iterated over using a foreach-statement.

Returns

An AliasSeq containing the values produced by iterating over iter.
Types
struct Impl
tmplApplyLeft(alias Template, args...)

Partially applies Template by binding its first (left) or last (right) arguments to args.

Behaves like the identity function when args is empty.

Parameters

Templatetemplate to partially apply
argsarguments to bind

Returns

_Template with arity smaller than or equal to Template
tmplApplyRight(alias Template, args...)

Ditto

tmplSmartAlias(T...)
tmplRepeat(size_t n, items...)

Creates an AliasSeq which repeats items exactly n times.

tmplstaticSort(alias cmp, items...)

Sorts an AliasSeq using cmp.

Parameters: cmp = A template that returns a bool (if its first argument is less than the second one) or an int (-1 means less than, 0 means equal, 1 means greater than)

items = The AliasSeq to sort

Returns

The sorted alias sequence
tmplstaticMerge(alias cmp, uint mid, items...)
tmplisLessEq(alias cmp, Seq...) if (Seq.length == 2)
tmplStride(int stepSize, Args...) if (stepSize != 0)

Selects a subset of Args by stepping with fixed stepSize over the sequence. A negative stepSize starts iteration with the last element.

Parameters

stepSizeNumber of elements to increment on each iteration. Can't be 0.
ArgsTemplate arguments.

Returns

An AliasSeq filtered by the selected stride.
tmplisSame(alias a, alias b)
tmplisSame(A, B)
tmplPack(T...)