Hi all,

Using the following example:

---------------

import std.stdio;

pure void foo()
{
    debug
    {
        stdout.writeln("1");
    }

    stdout.writeln("2");
}

void main(string[] args)
{
    foo();
}

---------------

Using either '-debug' or '-release', the second stdout will give an error (Error: pure function 'main.foo' cannot access mutable static data 'stdout') which is alright by me.

The question is why the first stdout doesn't throw the same error when compiling with the '-debug' option? Surely the issue will be the same and the debug-statement should be satisfied.


Ĝis,
Duarte

On 04/09/2017 10:49 PM, Duarte wrote:
> ---------------
>
> import std.stdio;
>
> pure void foo()
> {
>     debug
>     {
>         stdout.writeln("1");
>     }
>
>     stdout.writeln("2");
> }
>
> void main(string[] args)
> {
>     foo();
> }
>
> ---------------
>
> Using either '-debug' or '-release', the second stdout will give an
> error (Error: pure function 'main.foo' cannot access mutable static data
> 'stdout') which is alright by me.
>
> The question is why the first stdout doesn't throw the same error when
> compiling with the '-debug' option? Surely the issue will be the same
> and the debug-statement should be satisfied.

You're allowed to break purity in debug code.

From the spec: "As a concession to practicality, a pure function can also [...] perform impure operations in statements that are in a ConditionalStatement controlled by a DebugCondition"

https://dlang.org/spec/function.html#pure-functions

On Sunday, 9 April 2017 at 20:59:26 UTC, ag0aep6g wrote:
> On 04/09/2017 10:49 PM, Duarte wrote:
>> [...]
>
> You're allowed to break purity in debug code.
>
> From the spec: "As a concession to practicality, a pure function can also [...] perform impure operations in statements that are in a ConditionalStatement controlled by a DebugCondition"
>
> https://dlang.org/spec/function.html#pure-functions


Cheers mate!