On Wed, Jun 12, 2019 at 07:46:12PM +0000, Mek101 via Digitalmars-d-learn wrote: [...] > > public size_t indexOf(alias pred = "a == b", Range)(Range array) > > { > > alias predicate = unaryFun!pred; > > for(size_t i = 0; i < array.length; i++) > > if(predicate(array[i])) > > return i; > > return size_t.max; > > } > > Say that I may want to use the function in a @nogc scope, providing a > @nogc callable, but I also want to reuse the same code in managed > scope while passing a delegate: how can I apply the attributes of the > given callable to the function so that they're automatically > determined at compile time? [...]
You don't need to do anything special; indexOf, as you declared it, is already a template function, so the compiler should automatically apply attribute inference to it. So if pred is @nogc, and the implementation of indexOf itself doesn't invoke the GC, the compiler should automatically infer @nogc for you. One safeguard that you might want to consider is to write a @nogc unittest, something like this: @nogc unittest { ... auto result = indexOf!(...)(...); ... } The @nogc annotation on the unittest ensures that as long as the pred argument to indexOf is @nogc, indexOf itself will also be @nogc. This prevents future changes from accidentally introducing GC dependent code in the implementation of indexOf, while at the same time not explicitly marking indexOf as @nogc (only the unittest is annotated, not the function itself) allows you to use it with GC-dependent predicates as well. T -- Which is worse: ignorance or apathy? Who knows? Who cares? -- Erich Schubert