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Module `std.functional`

Functions that manipulate other functions.

This module provides functions for compile time function composition. These functions are helpful when constructing predicates for the algorithms in std.algorithm or std.range.


Function Name	Description
`adjoin`	Joins a couple of functions into one that executes the original functions independently and returns a tuple with all the results.
`compose`, `pipe`	Join a couple of functions into one that executes the original functions one after the other, using one function's result for the next function's argument.
`forward`	Forwards function arguments while saving ref-ness.
`lessThan`, `greaterThan`, `equalTo`	Ready-made predicate functions to compare two values.
`memoize`	Creates a function that caches its result for fast re-evaluation.
`not`	Creates a function that negates another.
`partial`	Creates a function that binds the first argument of a given function to a given value.
`reverseArgs`	Predicate that reverses the order of its arguments.
`toDelegate`	Converts a callable to a delegate.
`unaryFun`, `binaryFun`	Create a unary or binary function from a string. Most often used when defining algorithms on ranges.

Functions

Name	Description
`memoize(args)`	Memoizes a function so as to avoid repeated computation. The memoization structure is a hash table keyed by a tuple of the function's arguments. There is a speed gain if the function is repeatedly called with the same arguments and is more expensive than a hash table lookup. For more information on memoization, refer to this book chapter.
`partial(args2)`	Partially applies fun by tying its first argument to arg.
`toDelegate(fp)`	Convert a callable to a delegate with the same parameter list and return type, avoiding heap allocations and use of auxiliary storage.

Templates

Name	Description
`adjoin`	Takes multiple functions and adjoins them together. The result is a `Tuple` with one element per passed-in function. Upon invocation, the returned tuple is the adjoined results of all functions.
`binaryFun`	Transforms a string representing an expression into a binary function. The string must either use symbol names `a` and `b` as the parameters or provide the symbols via the `parm1Name` and `parm2Name` arguments. If `fun` is not a string, `binaryFun` aliases itself away to `fun`.
`binaryReverseArgs`	Binary predicate that reverses the order of arguments, e.g., given `pred(a, b)`, returns `pred(b, a)`.
`not`	Negates predicate `pred`.
`reverseArgs`	N-ary predicate that reverses the order of arguments, e.g., given `pred(a, b, c)`, returns `pred(c, b, a)`.
`unaryFun`	Transforms a string representing an expression into a unary function. The string must either use symbol name `a` as the parameter or provide the symbol via the `parmName` argument. If `fun` is not a string, `unaryFun` aliases itself away to `fun`.

Aliases

Name	Type	Description
`adjoin`	`F[0]`	Takes multiple functions and adjoins them together. The result is a `Tuple` with one element per passed-in function. Upon invocation, the returned tuple is the adjoined results of all functions.
`compose`	`unaryFun!(fun[0])`	Composes passed-in functions `fun[0], fun[1], ...` returning a function `f(x)` that in turn returns `fun[0](fun[1](...(x)))...`. Each function can be a regular functions, a delegate, or a string.
`equalTo`		Predicate that returns a == b. Correctly compares signed and unsigned integers, ie. !(-1 == ~0U).
`forward`	`fwd`	Forwards function arguments with saving ref-ness.
`greaterThan`		Predicate that returns a > b. Correctly compares signed and unsigned integers, ie. 2U > -1.
`lessThan`		Predicate that returns a < b. Correctly compares signed and unsigned integers, ie. -1 < 2U.
`pipe`	`compose!(Reverse!fun)`	Pipes functions in sequence. Offers the same functionality as `compose`, but with functions specified in reverse order. This may lead to more readable code in some situation because the order of execution is the same as lexical order.

Authors

Andrei Alexandrescu

License

Boost License 1.0.