Re: compiler error when trying to get random key from AA

[Basile B. via Digitalmars-d-learn]

On Saturday, 25 January 2020 at 08:35:18 UTC, mark wrote:

I have this code:

import std.random;
import std.stdio;
void main()
{
    auto aa = ["one": 1, "two": 2, "three": 3];
    writeln(aa);
    auto rnd = rndGen;
    auto word = aa.byKey.choice(rnd);
    writeln(word);
}

And in the D playground it gives this error:

onlineapp.d(8): Error: template std.random.choice cannot deduce function from argument types !()(Result, MersenneTwisterEngine!(uint, 32LU, 624LU, 397LU, 31LU, 2567483615u, 11LU, 4294967295u, 7LU, 2636928640u, 15LU, 4022730752u, 18LU, 1812433253u)), candidates are:

/dlang/dmd/linux/bin64/../../src/phobos/std/random.d(2599):

choice(Range, RandomGen = Random)(auto ref Range range, ref RandomGen urng)

  with Range = Result,

RandomGen = MersenneTwisterEngine!(uint, 32LU, 624LU, 397LU, 31LU, 2567483615u, 11LU, 4294967295u, 7LU, 2636928640u, 15LU, 4022730752u, 18LU, 1812433253u)

  must satisfy the following constraint:
       isRandomAccessRange!Range
/dlang/dmd/linux/bin64/../../src/phobos/std/random.d(2609):
 choice(Range)(auto ref Range range)

I am treating aa as a set and want to pick a random word from it.

What am I doing wrong?

I'm sorry I can't give a link to this code in the D playground but the URL in the web browser is just https://run.dlang.io/ and when I click Shorten to get a URL nothing seems to happen (using Firefox on Linux).

rndGen is a range.

Use `auto word = aa.byKey.choice(rnd.front())` as index instead.
Then `rndGen.popFront()` to advance.