What is the Time Complexity of Go\'s `len()` Function for Strings and Slices?

The Complexity of len() on Strings and Slices in Go

The len() function can be used to obtain the length of various data types in Go. Two commonly used data types are strings and slices. Understanding the complexity of len() on these data types is crucial for optimizing program performance.

Strings

A string in Go is an immutable sequence of Unicode code points. The length of a string is the number of code points it contains. Strings are represented internally by a structure that includes a pointer to the underlying array of code points and a length field. When calling len() on a string, Go simply reads the length field from this structure, making len() an O(1) operation.

Slices

A slice in Go is a dynamically sized, flexible array of elements of a specific type. Slices have a length, capacity, and a pointer to the underlying array of elements. The length of a slice is the number of elements currently allocated in the slice. The capacity is the maximum number of elements that can be held in the slice before needing to be reallocated.

Similar to strings, the len() function on a slice returns the length field from the slice header, which contains the length, capacity, and pointer to the underlying array. This makes the len() call on slices also an O(1) operation.

Conclusion

The len() function has O(1) complexity for both strings and slices in Go. This efficiency is due to the way these data types are stored internally, with the length being readily available in their respective headers.

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