The D Programming Language's Unofficial Docs
beta
The D Programming Language's Unofficial Docs
beta
the predicate function(s) to apply to the elements
1 immutable arr = [1, 2, 3, 4, 5]; 2 3 // Sum all elements 4 assert(arr.fold!((a, b) => a + b) == 15); 5 6 // Sum all elements with explicit seed 7 assert(arr.fold!((a, b) => a + b)(6) == 21); 8 9 import std.algorithm.comparison : min, max; 10 import std.typecons : tuple; 11 12 // Compute minimum and maximum at the same time 13 assert(arr.fold!(min, max) == tuple(1, 5)); 14 15 // Compute minimum and maximum at the same time with seeds 16 assert(arr.fold!(min, max)(0, 7) == tuple(0, 7)); 17 18 // Can be used in a UFCS chain 19 assert(arr.map!(a => a + 1).fold!((a, b) => a + b) == 20); 20 21 // Return the last element of any range 22 assert(arr.fold!((a, b) => b) == 5);
Implements the homonym function (also known as accumulate, compress, inject, or foldl) present in various programming languages of functional flavor. The call fold!(fun)(range, seed) first assigns seed to an internal variable result, also called the accumulator. Then, for each element x in range, result = fun(result, x) gets evaluated. Finally, result is returned. 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).