Re: Faking a non-pure function as pure

[Nordlöw via Digitalmars-d-learn]

On Friday, 16 February 2018 at 18:03:40 UTC, Ali Çehreli wrote:

auto pureF = assumePure();
pureF(42);

Ali


Thanks!

Re: Faking a non-pure function as pure

[Ali Çehreli via Digitalmars-d-learn]

On 02/16/2018 09:58 AM, Nordlöw wrote:


void g() pure
{
     static assert(!__traits(compiles, { auto x = f(42); }));
     alias pureF = assumePure!(typeof());
     // TODO: how do I call pureF?
     // auto x = (*pureF)(42);
     // auto x = pureF(42);
}



auto pureF = assumePure();
pureF(42);

Ali

Faking a non-pure function as pure

[Nordlöw via Digitalmars-d-learn]

I'm struggling with my definition of assumePure that should make 
a non-pure function `f` callable as pure `pureF`.


I've copied the definition of assumePure from the Phobos docs at

https://dlang.org/phobos/std_traits.html#SetFunctionAttributes

and managed to define pureF using it but I cannot call `pureF` as 
either


auto x = (*pureF)(42);
auto x = pureF(42);

How do I do that?

import std.traits : isFunctionPointer, isDelegate, 
functionAttributes, FunctionAttribute, SetFunctionAttributes, 
functionLinkage;


/** Return `T` assumed to be `pure`.
Copied from 
https://dlang.org/phobos/std_traits.html#SetFunctionAttributes.

*/
auto assumePure(T)(T t)
if (isFunctionPointer!T || isDelegate!T)
{
enum attrs = functionAttributes!T | FunctionAttribute.pure_;
return cast(SetFunctionAttributes!(T, functionLinkage!T, 
attrs)) t;

}

int f(int x)
{
return x + 1;
}

void g() pure
{
static assert(!__traits(compiles, { auto x = f(42); }));
alias pureF = assumePure!(typeof());
// TODO: how do I call pureF?
// auto x = (*pureF)(42);
// auto x = pureF(42);
}