• Atila Neves (5/5) Mar 26 2014 Why the (inout int = 0) instead of an empty parameter list? I
• Atila Neves (2/9) Mar 28 2014
• Dicebot (4/14) Mar 28 2014 Friend of mine (learning D) has recently asked same question and
• Andrej Mitrovic (22/23) Mar 28 2014 Try removing it and compile std.range with -unittest. Here's what happen...

"Atila Neves" <atila.neves gmail.com> writes:

Why the (inout int = 0) instead of an empty parameter list? I
checkout how isInputRange was implemented and I copied the idiom,
but I'd like to know why it's like that instead of cargo culting.
Thanks,

Atila

"Atila Neves" <atila.neves gmail.com> writes:

Seriously, nobody? I'd've thought this was quite important.

On Thursday, 27 March 2014 at 05:27:50 UTC, Atila Neves wrote:
 Why the (inout int = 0) instead of an empty parameter list? I
 checkout how isInputRange was implemented and I copied the 
 idiom,
 but I'd like to know why it's like that instead of cargo 
 culting.
 Thanks,

 Atila

"Dicebot" <public dicebot.lv> writes:

On Friday, 28 March 2014 at 11:17:10 UTC, Atila Neves wrote:
 Seriously, nobody? I'd've thought this was quite important.

 On Thursday, 27 March 2014 at 05:27:50 UTC, Atila Neves wrote:
 Why the (inout int = 0) instead of an empty parameter list? I
 checkout how isInputRange was implemented and I copied the 
 idiom,
 but I'd like to know why it's like that instead of cargo 
 culting.
 Thanks,

 Atila


Friend of mine (learning D) has recently asked same question and 
I failed to answer :( I never use it in constraint checks (empty 
parameter list instead) and have not encountered any issue.

Andrej Mitrovic <andrej.mitrovich gmail.com> writes:

On 3/27/14, Atila Neves <atila.neves gmail.com> wrote:
 Why the (inout int = 0) instead of an empty parameter list?

Try removing it and compile std.range with -unittest. Here's what happens:

std\range.d(546): Error: static assert  (isInputRange!(inout(int)[])) is false

The reason it's false is because the code wouldn't compile. Here's a test-case:

-----
import std.array;

void test()
{
    inout(int)[] r = (inout(int)[]).init;
    if (r.empty) {}
    r.popFront();
    auto h = r.front;
}

void main()
{
    test();
}
-----

test.d(7): Error: variable test.test.r inout variables can only be
declared inside inout functions

So you need to add inout in the parameter list to avoid this compiler
error and to make your function work with any qualified range type.