On Sunday, 18 December 2016 at 13:14:08 UTC, Picaud Vincent wrote:
Reading std/bigint.d code:
https://github.com/dlang/phobos/blob/00c1cc3b0d354363793c8b419ce84da722578138/std/bigint.d#L589
I have seen this:
bool opEquals()(auto ref const BigInt y) const pure @nogc
{
return sign == y.sign && y.data == data;
}
my problem is that I do not understand the role/meaning of
"auto" in this context.
With auto ref, the parameter can be either a LValue or a RValue.
When passing a struct as auto ref, it's taken as ref.
for example:
struct Foo{this(this){writeln("copy");}}
struct Bar{@disable this(this);}
void testAsRef(T)(ref T t){}
void testAsValue(T)(T t){}
void testRefOrValue(T)(auto ref T t){}
Foo foo;
Bar bar;
testAsRef(1); // error 1 is not ref
testAsRef(foo); // ok, not copied
testAsRef(bar); // ok, not copied
testAsValue(1); // ok
testAsValue(foo); // ok but copied
testAsValue(bar); // error, could only be copied but postblit is
disabled
testRefOrValue(1); // ok, not taken as ref
testRefOrValue(foo); // ok, not copied
testRefOrValue(bar); // ok, taken as ref
As you can see, auto ref is more flexible with the parameter.
This make sense for templated functions.
