one or more functions of the form Acc function(Acc, ElemT)
immutable arr = [1, 2, 3, 4, 5]; // Sum all elements assert(arr.fold!((a, e) => a + e) == 15); // Sum all elements with explicit seed assert(arr.fold!((a, e) => a + e)(6) == 21); import std.algorithm.comparison : min, max; import std.typecons : tuple; // Compute minimum and maximum at the same time assert(arr.fold!(min, max) == tuple(1, 5)); // Compute minimum and maximum at the same time with seeds assert(arr.fold!(min, max)(0, 7) == tuple(0, 7)); // Can be used in a UFCS chain assert(arr.map!(a => a + 1).fold!((a, e) => a + e) == 20); // Return the last element of any range assert(arr.fold!((a, e) => e) == 5);
* Fold (higher-order function)
* sum is similar to fold!((a, b) => a + b) that offers precise summing of floating point numbers.
* fold is functionally equivalent to reduce with the argument order reversed, and without the need to use `tuple` for multiple seeds.
Implements the homonym function (also known as accumulate, compress, inject, or foldl) present in various programming languages of functional flavor, iteratively calling one or more predicates.
Each predicate in fun must take two arguments:
* An accumulator value * An element of the range r
Each function must return a value which implicitly converts to the type of the accumulator.
For a single function, the call fold!(fun)(range, seed) will:
* Use seed to initialize an internal accumulator. * For each element e in range, evaluate accumulator = fun(result, e). * Return accumulator.
The one-argument version fold!(fun)(range) works similarly, but it uses the first element of the range as the seed (the range must be non-empty) and iterates over the remaining elements.
Multiple results are produced when using multiple functions.
If range has only one element, the functions are never invoked and result and the seed is returned unchanged.