`str &= data` doesn't behave as `str = str & data`.

[kayabaNerve]

If a string and an int are combined via &, a compilation error occurs. When combined via &=, the int is converted to a string via $ and the code compiles. This error doesn't occur in Nimscript, and is localized to Nim.

var
    a: string = "abc"
    b: int = 5
a &= b
echo a

Current Output

abc5

Expected Output

Compilation Error of Error: type mismatch: got <string, int>

Tested on 0.19.0, 0.19.4, and devel (compiled as this issue was written). All three had Nimscript (tested via nim secret) throw an error, but Nim compile.

[PMunch]

According to Araq on IRC this is caused by an add proc that takes a string and an int, which I assume is this one: https://nim-lang.org/0.19.2/system.html#add%2Cstring%2Cint64

EDIT: And the rewrite seems to happen here: https://github.com/nim-lang/Nim/blob/master/lib/system.nim#L3822 commenting out that and adding a procedure that takes string + char works fine for compiling Nim itself. Not sure if any library out there uses this though..

[mratsim]

I think a & overload for string, int should be in sugar.nim or lenientops.nim, same thing for &=.

Tagging RFC as it's more of a system.nim / standard library design question.