How are Go Closures Represented in Memory?

Memory Layout of Closures in Go

Go functions, including closures, implement lexical scoping, allowing them to reference variables declared in their enclosing scope. This behavior begs the question of how these closures are represented in memory.

In Go, closures are essentially variables that reference the environment in which they were created. The allocated memory for a closure consists of:

• A pointer to the function's code
• A set of references to the variables that the closure captures from the enclosing scope

The size of the memory allocated for a closure depends on the platform and architecture, but it typically involves:

• 8 bytes for the code pointer (on 64-bit systems)
• 8 bytes per captured variable

For example, consider the following closure:

type M int

func (m *M) Adder(amount int) func() {
    return func() {
        *m = *m + amount
    }
}

When code calls a := m.Adder(), two closures are created:

1. The first closure captures amount from the enclosing scope.
2. The second closure captures a, which references m, capturing m indirectly.

The memory layout of the first closure will consist of:

• 8 bytes for the function code pointer
• 4 bytes for amount (assuming int is 32 bits)

The total memory allocated will be 16 bytes.

The memory layout of the second closure will consist of:

• 8 bytes for the function code pointer
• 8 bytes for a, which points to the first closure
• 8 bytes for (*m).Adder(amount)

The total memory allocated will be 24 bytes.

In summary, Go closures are implemented on the heap and store a pointer to the function code as well as references to captured variables. The size of the allocated memory depends on the number of captured variables and the platform architecture.

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