front evaluated multiple time with joiner depending on where extra arg given

[bearophile]

Timothee Cour:

>     auto b=[1,2,3].map!(a=>{counter++; return 
> [a];}()).joiner([0]).array;

Currently there are some problems inside some of the higher order 
functions of Phobos. So as general rule don't put impure code 
inside the functions (usually lambdas) you pass to the higher 
order functions like map, filter, etc.

By the way, a more readable way to put more commands inside a 
lambda should be:

(a){ counter++; return [a]; }

Bye,
bearophile