www.digitalmars.com         C & C++   DMDScript  

digitalmars.D.learn - Querying parameter passing semantics for `auto ref const` variables

reply =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:
Is there a way to query at compile-time whether a call to

     f(T)(auto ref const T x)

passed the variable `x` from a l-value or r-value?

A call to `isRef!T` inside the function `f` is always `false` for 
`l-value` and `r-value` passing.

I need this to detect automatic delayed evaluation of 
sub-expressions in my GNU MP wrapper at

https://github.com/nordlow/gmp-d
Jan 15
next sibling parent =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:
On Sunday, 15 January 2017 at 14:33:25 UTC, Nordlöw wrote:
 Is there a way to query at compile-time whether a call to
Further, overloading such as struct S { int x, y; } static f(in S s) {} static f(const ref S s) {} f(S.init); S s; f(s); fails as declaration f is already defined
Jan 15
prev sibling parent reply kinke <noone nowhere.com> writes:
On Sunday, 15 January 2017 at 14:33:25 UTC, Nordlöw wrote:
 A call to `isRef!T` inside the function `f` is always `false` 
 for `l-value` and `r-value` passing.
According to https://dlang.org/spec/template.html#auto-ref-parameters, it should be `__traits(isRef, x)`.
Jan 15
parent reply =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:
On Sunday, 15 January 2017 at 17:00:41 UTC, kinke wrote:
 On Sunday, 15 January 2017 at 14:33:25 UTC, Nordlöw wrote:
 A call to `isRef!T` inside the function `f` is always `false` 
 for `l-value` and `r-value` passing.
According to https://dlang.org/spec/template.html#auto-ref-parameters, it should be `__traits(isRef, x)`.
This struct S { int x, y; } void f()(auto ref const S s) { pragma(msg, "type:", typeof(s), " isRef:", isRef!s); } f(S.init); S s; f(s); prints type:const(S) isRef:false type:const(S) isRef:true I made the mistake of incorrectly using isRef!S when I should have used isRef!s Thanks!
Jan 15
parent =?UTF-8?B?Tm9yZGzDtnc=?= <per.nordlow gmail.com> writes:
On Sunday, 15 January 2017 at 17:41:36 UTC, Nordlöw wrote:
 This

     struct S { int x, y; }
     void f()(auto ref const S s)
     {
         pragma(msg, "type:", typeof(s), " isRef:", isRef!s);
     }
     f(S.init);
     S s;
     f(s);

 prints

     type:const(S) isRef:false
     type:const(S) isRef:true
given that enum isRef(alias fn) = __traits(isRef, fn); :)
Jan 15