Mistake #22 "nil vs empty slices" regarding memory allocation of empty slices about 100-go-mistakes HOT 3 CLOSED

The empty slice itself doesn't need memory allocation, but when Initializing it, we also need to initialize the slice header, which contains a pointer(array) that needs memory allocations. zerobase is the base address for all 0-byte allocations, but itself is not 0.

from 100-go-mistakes.

@wureny

I am not really proficient in Assembly, but looking at the code, the only difference is which value gets stored in AX register.

Assembler for nil slice:

XORL	AX, AX // zeroing
XORL	BX, BX // zeroing
MOVQ	BX, CX	

Assembler for empty slice:

LEAQ	runtime.zerobase(SB), AX // take address
XORL	BX, BX // zeroing
MOVQ	BX, CX

Compiled for GOOS=linux GOARCH=AMD64

from 100-go-mistakes.