compiler error when trying to get random key from AA

[Basile B.]

On Saturday, 25 January 2020 at 09:18:01 UTC, Basile B. wrote:
> 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).
>
> So the problem is that byKey is not a ref parameter, so you can 
> use array on it:

Well the explanation for your error is rather that byKey did not 
verify isRandomAccesRange, i.e indexable by an index so .array on 
it solve this.
pfff finally ...