Reading an environment variable value

Jun 29, 2023

Josh Holtrop

Jun 29, 2023

Adam D Ruppe

Jun 29, 2023

Josh Holtrop

June 29, 2023

Reading an environment variable value

Posted by Josh Holtrop

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Josh Holtrop

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I am trying to use std.process.environment.get() as described here: https://dlang.org/library/std/process/environment.get.html

I wrote this program to test it:

import std.stdio;
import std.process;

int main(string[] args)
{
    string home = environment.get("HOME");
    writeln("home is ", home);
    return 0;
}

But it fails to compile:

$ ldc2 -of environment environment.d
environment.d(6): Error: template `object.get` cannot deduce function from argument types `!()(string)`
/usr/lib/ldc/x86_64-linux-gnu/include/d/object.d(3230):        Candidates are: `get(K, V)(inout(V[K]) aa, K key, lazy inout(V) defaultValue)`
/usr/lib/ldc/x86_64-linux-gnu/include/d/object.d(3237):                        `get(K, V)(inout(V[K])* aa, K key, lazy inout(V) defaultValue)`

It works, though, to switch to a static import of std.process:

import std.stdio;
static import std.process;

int main(string[] args)
{
    string home = std.process.environment.get("HOME");
    writeln("home is ", home);
    return 0;
}

Why? What am I doing wrong in the first version that does not use the static import?

My ldc2 version:

$ ldc2 -version
LDC - the LLVM D compiler (1.28.0):
  based on DMD v2.098.0 and LLVM 11.1.0
  built with LDC - the LLVM D compiler (1.28.0)
  Default target: x86_64-pc-linux-gnu
  Host CPU: skylake
  http://dlang.org - http://wiki.dlang.org/LDC

On Thursday, 29 June 2023 at 18:47:48 UTC, Josh Holtrop wrote: > $ ldc2 -of environment environment.d Since you named the file `environment.d` and didn't use an explicit `module name.thing;` declaration, the compiler assumes it should match the filename. So it injects an implicit `module environment;` to the top of the file. Now when you mention `environment`, it uses *that* name instead of the imported name, so it thinks you are trying to pass it the module called environment instead of the object. If you add `module yourapp.environment;` or something to the top it'd fix it (unless you tried to use something called `yourapp`, then the name might conflict again!) or rename the file.

On Thursday, 29 June 2023 at 19:19:21 UTC, Adam D Ruppe wrote: > On Thursday, 29 June 2023 at 18:47:48 UTC, Josh Holtrop wrote: >> $ ldc2 -of environment environment.d > > Since you named the file `environment.d` and didn't use an explicit `module name.thing;` declaration, the compiler assumes it should match the filename. > > So it injects an implicit `module environment;` to the top of the file. > > Now when you mention `environment`, it uses *that* name instead of the imported name, so it thinks you are trying to pass it the module called environment instead of the object. > > If you add `module yourapp.environment;` or something to the top it'd fix it (unless you tried to use something called `yourapp`, then the name might conflict again!) > > or rename the file. Ah, that makes sense, and yes that fixed it. Thank you!

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