Why does the built-in function len in Go return int instead of uint?

Why does the Go language len function return int instead of uint ?

The built-in function len of Go language is used to return the length of various types (arrays, slices, maps, strings, channels). The official documentation clearly states that len function returns int type rather than an intuitively more appropriate uint (unsigned integer). This design choice is not accidental, and there are deep reasons behind it.

The description of the len function in the Go language specification is as follows:

 // The len built-in function returns the length of v, according to its type:
//
// Array: the number of elements in v.
// Pointer to array: the number of elements in *v (even if v is nil).
// Slice, or map: the number of elements in v; if v is nil, len(v) is zero.
// String: the number of bytes in v.
// Channel: the number of elements queued (unread) in the channel buffer;
// if v is nil, len(v) is zero.
//
// For some arguments, such as a string literal or a simple array expression, the
// result can be a constant. See the Go language specification's "Length and
// capacity" section for details.
func len(v Type) int

Although lengths are usually non-negative, there are several key considerations to choose int over uint :

1. Avoid the trap of unsigned integer operations: uint operations follow the modulo 2 ⁿ rule, for example, the result of 0 - 1 is not -1, but a large positive number. This is contrary to intuition and can easily lead to program errors.

2. Security is not an improvement: using uint does not improve program security. -1 and maximum uint values ​​may have the same effect in some cases, which may also cause problems.

3. The complexity of range check remains unchanged: whether int or uint is used, range checks are required, and there is no significant difference in workload.

4. Potential Optimization Advantages: In some cases, int type operations may be easier to compiler optimization.

5. Code consistency and readability: Using int maintains the consistency of code style and avoids the complexity brought about by mixing int and uint . Go language emphasizes simplicity and consistency, int , as a general integer type, is more in line with this design concept.

In summary, Go language designers chose int as the return type of len function in order to avoid potential traps of uint and maintain the consistency and readability of the code, rather than simply pursuing the superficial phenomenon of "length is not negative". This reflects Go's careful design and prediction of potential problems.

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