C# Feature - Local functions

Overview

Local functions let you define a named helper inside a method, which keeps implementation details close to the calling code.

Introduced In

C# 7.0 (2017)

Before

private bool IsValid(string candidate) => candidate.Length >= 3;

After

void Process(string value)
{
  if (!IsValid(value)) return;

  bool IsValid(string candidate) => candidate.Length >= 3;
}

Gotchas & Best Practices

• Prefer a local function when the helper needs a name and belongs only to one outer method.
• Use static local functions when no outer variables are needed.