C++ equivalent of Java's andThen() function to composite new function

Question

In Java, you can do the following code:

Function<Integer, Integer> times2 = e -> e * 2;
Function<Integer, Integer> squared = e -> e * e; 
times2.andThen(squared).apply(4);

What's C++'s equivalent of andThen() to coin/composite new functors? Thanks.

There isn't one. You'll have to find a library or build it yourself. — NathanOliver, Aug 22 '18 at 15:04
Does this question address your need? https://stackoverflow.com/questions/19071268/function-composition-in-c-c11 — rtpax, Aug 22 '18 at 15:05

score 2 · Accepted Answer · answered Aug 22 '18 at 15:22

If you are open to using Boost, then Boost.HOF is what you need. HOF (Higher order functions) provides the compose function adapter with the following semantics

assert(compose(f, g)(xs...) == f(g(xs...)));

In your case, you will do

auto composed = compose(squared, times2);
auto result = composed(4);

Have a look at the documentation for details https://www.boost.org/doc/libs/1_68_0/libs/hof/doc/html/include/boost/hof/compose.html

score 0 · Answer 2 · answered Aug 22 '18 at 15:05

0

Why not keep things simple?

int times2thenSquared(int x) {
    x = times2(x);
    return squared(x);
}

(can do it with lambda as well, if you want)

answered Aug 22 '18 at 15:05

Anton Malyshev

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C++ equivalent of Java's andThen() function to composite new function

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