How to work around the infamous dual-context when using delegates together with std.parallelism

[Christian Köstlin via Digitalmars-d-learn]

I have this small program here

test.d:
```
import std;
string doSomething(string[] servers, string user) {
    return user ~ servers[0];
}
void main() {
    auto servers = ["s1", "s2", "s3"];
    auto users = ["u1", "u2", "u3"];
    writeln(map!(user => servers.doSomething(user))(users));
    writeln(taskPool.amap!(user => servers.doSomething(user))(users));
}
```
The first map just works as expected, for the parallel amap though fromo 
(https://dlang.org/phobos/std_parallelism.html) I get the following 
warning with dmd:

```
/Users/.../dlang/dmd-2.096.1/osx/bin/../../src/phobos/std/parallelism.d(1711): 
Deprecation: function `test.main.amap!(string[]).amap` function requires 
a dual-context, which is deprecated
```

for ldc the build fails with:
```
/Users/.../dlang/ldc-1.26.0/bin/../import/std/parallelism.d(1711): 
Deprecation: function `test.main.amap!(string[]).amap` function requires 
a dual-context, which is deprecated
test.d(9):        instantiated from here: `amap!(string[])`
/Users/.../dlang/ldc-1.26.0/bin/../import/std/parallelism.d(1711): 
Error: function `test.main.amap!(string[]).amap` requires a 
dual-context, which is not yet supported by LDC
```


Thanks in advance for you insights,
Christian