The Status Nim style guide

return keyword [language.return]

Use return for returning early from a function, for example to reduce nesting.

In other cases, prefer implicit return expressions.

func f(v: ref Xxx): int =
  if v == nil:
    # early return to reduce nesting of happy case
    return 0
  ...

  # Prefer implicit return expressions in most other cases
  if conditions:
    v[].value
  else:
    0

func short(): int =
  42 # simple expressions also qualify

Pros

• Can simplify complex conditions and nesting
• Explicitly shows where return control flow hapens

Cons

• Brittle due to lack of compile-time enforcement of exhaustiveness of control flow and initialization
• When nested deeply, can make conditions for early return difficult to understand
• Surprising semantics in templates and macros

Practical notes

• beware of return in templates since the return happens after template expansion!
  • ...especially when changing a proc to a template
• return deep inside a complex set of conditionals indicates that the function likely needs refactoring
• return of a var risks returning instances that have not been fully initialized
  • this in particular applies to the implicit result variable.
• return expr is shorthand for result = expr; return result - this reduces to return result when there is no expression