How Does Go Handle String Comparison Under the Hood?

Go's Approach to String Comparison

In Go, string comparison is performed seamlessly without the use of any dedicated functions. However, a closer examination reveals that the Go runtime plays an active role behind the scenes.

Runtime Function Exploration

As illustrated in the assembly dump below, when Go compares two string literals, it initially checks if they reside at the same memory location. If this is not the case, it delegates the comparison task to the runtime.eqstring function. This function compares the lengths of the strings and then proceeds to do a byte-by-byte comparison.

...
0006 (foo.go:5) LEAQ    go.string."world"+0(SB),BX
0007 (foo.go:5) MOVQ    (BX),DX
0008 (foo.go:5) MOVQ    8(BX),AX
0009 (foo.go:6) JMP     ,11
0010 (foo.go:6) MOVQ    ,AX
0011 (foo.go:6) JMP     ,23
0012 (foo.go:6) CMPQ    CX,AX
0013 (foo.go:6) JNE     ,22
...
0017 (foo.go:6) CALL    ,runtime.eqstring+0(SB)
...

Implications for Developers

Unless one is involved in the development or optimization of the Go compiler or runtime, this technical detail is not of significant concern. Developers can continue to utilize the string comparison operators defined in the Go specification, confident that the runtime will efficiently handle the comparison process, with a time complexity of O(n), where n is the length of the strings being compared.

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