CODEWITHSUNDEEP
syntaxreturn-typenim-lang
Sod Almighty
Sod Almighty

Reputation: 1786

How to have multiple (alternate) return types in Nim?

I can declare a proc to return a "union type", but cannot actually return values of more than one type:

proc test(b: bool) : int|string =
 if b: 1 else: "hello"
  
echo test true
echo test false

Expected:

1
hello

Actual:

Error: type mismatch: got 'string' for '"hello"' but expected 'int literal(1)'

Even if I swap the return types (string|int) the error is the same. I am only allowed to return an int. I tried putting the return type in parens; and I tried using or instead of |. No dice.

What am I missing? (I don't want to use a variant object.)

The code can be tested online at the Nim Playground. I've scoured google and the Nim documentation, and come up empty.

Upvotes: 1

Views: 749

Answers (1)

PMunch
PMunch

Reputation: 1719

Return types have to be known at compile time in Nim. Imagine you tried to return the result of that procedure to a string variable. Now you're in a scenario where one return value works, but the other would be a compilation error. In order to allow Nim to figure out whether to throw an error or not it must be able to figure out which type will be returned at compile time. The solution here is to use a static[bool] and a when in place of the if. If you actually need a type that can hold different types on runtime you have to use variant objects.

Upvotes: 4

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