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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` `Instantiate`

References

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

Templates

Name	Description
`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.
`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.

Manifest constants

Name	Type	Description
`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])`.
`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.
`staticIsSorted`		Checks if an `AliasSeq` is sorted according to `cmp`.

Aliases

Name	Type	Description
`Alias`	`a`	Allows `alias`ing 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.
`aliasSeqOf`	`AliasSeq!()`	Converts an input range `range` to an alias sequence.
`DerivedToFront`	`TList`	Returns the `AliasSeq` TList with the types sorted so that the most derived types come first.
`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.
`Filter`	`AliasSeq!()`	Filters an `AliasSeq` using a template predicate. Returns a `AliasSeq` of the elements which satisfy the predicate.
`Instantiate`	`Template!Params`	Instantiates the given template with the given list of parameters.
`MostDerived`	`T`	Returns the type from TList that is the most derived from type T. If none are found, T is returned.
`NoDuplicates`	`AliasSeq!(fst,EraseAllN!(fst.length,fst,snd))`	Returns an `AliasSeq` created from TList with the all duplicate types removed.
`Repeat`	`AliasSeq!()`	Creates an `AliasSeq` which repeats a type or an `AliasSeq` exactly `n` times.
`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.
`Reverse`	`TList`	Returns an `AliasSeq` created from TList with the order reversed.
`staticMap`	`AliasSeq!()`	Evaluates to `AliasSeq!(F!(T[0]), F!(T[1]), ..., F!(T[$ - 1]))`.
`staticSort`	`Seq`	Sorts a `AliasSeq` using `cmp`.
`Stride`	`AliasSeq!()`	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.

Authors

Walter Bright, David Nadlinger

License

Boost License 1.0.