outvars

Outvars, short for out variables, are a programming construct used as out parameters in languages that support an out keyword. They enable a method to return additional values beyond its primary return value by assigning to a declared variable passed by reference. In particular, C# supports out parameters and, since version 7.0, allows inline declaration of an out variable as part of the method call.

How they work: An out parameter is passed by reference, and the called method is required to assign a value to it before returning. The caller does not need to initialize the variable before the call; after the call completes, the out parameter holds the value assigned by the callee. Inline declarations via out var are common in C# 7.0 and later, enabling patterns such as int.TryParse(s, out var number) or dict.TryGetValue(key, out var value). The scope of the declared out variable typically extends to the enclosing block, making the variable usable after the call within that block.

Use cases: Outvars are useful for methods that need to return more than one result without creating a separate result type. They are frequently used in parsing, lookups, and conditional patterns where a boolean success flag is returned alongside the converted or retrieved value. They can help reduce boilerplate by avoiding extra temporary variables.

Considerations: Overuse can hamper readability, especially when multiple out parameters are involved. Some developers prefer dedicated result types, tuples, or simple return values for clarity. Inline out variable declarations may alter scoping and lifetime expectations, so it is important to understand language-specific rules.

Compatibility and alternatives: The exact behavior of outvars is language-specific. In C#, out parameters and inline out var declarations are part of the language since version 7.0, with variations in syntax across versions. Alternatives include tuple returns, custom result types, or ref/out patterns in languages that support them.