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Module std.meta

Templates to manipulate template argument lists (also known as type lists).

Some operations on alias sequences are built in to the language, such as TL[n] which gets the nth type from the alias sequence. TL[lwr .. upr] returns a new type list that is a slice of the old one.

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

References

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

Templates

Name Description
aliasSeqOf Converts an input range range to an alias sequence.
allSatisfy Tests whether all given items satisfy a template predicate, i.e. evaluates to F!(T[0]) && F!(T[1]) && ... && F!(T[$ - 1]).
anySatisfy Tests whether any given items satisfy a template predicate, i.e. evaluates to F!(T[0]) || F!(T[1]) || ... || F!(T[$ - 1]).
ApplyLeft Partially applies Template by binding its first (left) or last (right) arguments to args.
ApplyRight Partially applies Template by binding its first (left) or last (right) arguments to args.
DerivedToFront Returns the AliasSeq TList with the types sorted so that the most derived types come first.
Filter Filters an AliasSeq using a template predicate. Returns a AliasSeq of the elements which satisfy the predicate.
MostDerived Returns the type from TList that is the most derived from type T. If none are found, T is returned.
NoDuplicates Returns an AliasSeq created from TList with the all duplicate types removed.
Repeat Creates an AliasSeq which repeats a type or an AliasSeq exactly n times.
Reverse Returns an AliasSeq created from TList with the order reversed.
staticIsSorted Checks if an AliasSeq is sorted according to cmp.
staticMap Evaluates to AliasSeq!(F!(T[0]), F!(T[1]), ..., F!(T[$ - 1])).
staticSort Sorts a AliasSeq using cmp.
Stride Selects a subset of the argument list by stepping with fixed stepSize over the list. A negative stepSize starts iteration with the last list element.
templateAnd 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.
templateNot Negates the passed template predicate.
templateOr 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.

Enum values

Name Type Description
staticIndexOf Returns the index of the first occurrence of type T in the sequence of zero or more types TList. If not found, -1 is returned.

Aliases

Name Type Description
Alias a Allows aliasing of any single symbol, type or compile-time expression.
AliasSeq TList Creates a sequence of zero or more aliases. This is most commonly used as template parameters or arguments.
Erase GenericErase!(T,TList) Returns an AliasSeq created from TList with the first occurrence, if any, of T removed.
EraseAll GenericEraseAll!(T,TList) Returns an AliasSeq created from TList with the all occurrences, if any, of T removed.
Replace GenericReplace!(T,U,TList) Returns an AliasSeq created from TList with the first occurrence of type T, if found, replaced with type U.
ReplaceAll GenericReplaceAll!(T,U,TList) Returns an AliasSeq created from TList with all occurrences of type T, if found, replaced with type U.

Authors

Walter Bright, David Nadlinger

License

Boost License 1.0.

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