Why Can\'t I Slice a Function\'s Return Value in Go?

Understanding the Difference in Behavior of Variables and Function Return Values

In the provided code, the intention is to join two lines of code that perform a specific operation. However, the second attempt results in an error.

Error Occurs in the 2nd Case

The error message "models/models.go:104: invalid operation sha1.Sum(([]byte)(uf.Pwd))[:] (slice of unaddressable value)" suggests a problem with slicing in the second case. Specifically, attempting to slice the return value of the function call sha1.Sum() is causing the issue.

Reason for the Issue

Function return values in Go are not addressable, meaning they cannot be used as operands in operations that require addressability. In this case, slicing an array requires the array to be addressable.

Function Return Values

Only the following entities in Go are addressable:

• Variables
• Pointer indirections
• Slice indexing operations
• Field selectors of addressable structs
• Array indexing operations of addressable arrays

Solution and First Case

The first case works correctly because the return value of sha1.Sum() is first stored in a local variable (hash) which is addressable. This local variable can then be used in subsequent operations, including slicing.

Conclusion

To avoid errors like the one encountered in the 2nd case, it is important to understand the addressability rules in Go. Function return values are not addressable, and slicing requires the array operand to be addressable.

The above is the detailed content of Why Can\'t I Slice a Function\'s Return Value in Go?. For more information, please follow other related articles on the PHP Chinese website!