When does the Go compiler place variables on the heap and the stack ?

• Sharing gown typically stays on the stack
  • Passing references down as function parameters
• Sharing up typically escapes to the heap
  • Returning references (pointers) from functions
• "typically": only the compiler knows.

When are values constructed on the heap ?

1. When a value could possibly be referenced after the function that constructed the values returns.
2. When the compiler determines a value is too large to fit on the stack.
3. When the compiler does not know the size of a value at compile time.

Points to remember

• Optimize for correctness, not performance
• Go only puts function variables on the stack if it can prove a variable is not used after the function returns
• Sharing down typically stays on the stack
• Sharing up typically escapes to the heap
• You want to know ? Ask the compiler to find out using the tooling