The impact of T vs. t in Golang performance optimization

In Go performance optimization, the alias (uppercase letter T) can be exported to point to the original type, resulting in pointer dereference and stack allocation overhead; the alias (lowercase letter t) cannot be exported and the original type can be used directly, avoiding these overheads. This improves performance. Specifically: Exportable aliases implicitly generate pointers to primitive types, incurring pointer dereference overhead. Exportable aliases are allocated on the stack within a function, while primitive types are allocated in registers, which adds overhead when the function is called frequently.

The impact of T vs. t in Golang performance optimization

In Golang, type aliases use type Keyword definition allows developers to create an alias pointing to an existing type. This means that the aliased type has the same underlying representation and behavior as the original type.

Although type aliases are generally only used to improve readability and maintainability of code, they can also have an impact on performance in some cases. In particular, there are key differences between aliases defined using lowercase and/or uppercase letters.

T vs. t

Type aliases defined using uppercase letters (T) are exportable aliases, This means it can be accessed from outside the package. On the other hand, a type alias defined with lowercase letters (t) named is not an exportable alias and can only be accessed within the package in which it is defined.

Performance Difference

Exportable aliases implicitly generate a pointer to the primitive type, which means that each time an exportable alias is used, a layer of pointer resolution is generated Quote. In contrast, non-exportable aliases do not generate pointers, but instead use the underlying representation of the primitive type directly.

This difference can cause a performance impact in the following situations:

• Pointer arithmetic: When using exportable aliases, any pointer arithmetic will occur during the build On pointer types, this will be slower than operating on pointers on primitive types.
• Stack allocation: When using an exportable alias in a function, the alias type will be allocated on the stack, while the original type will be allocated in a register. This causes additional overhead when the function is called frequently.

Practical case

Consider the following code snippet:

// 可导出别名
type T = time.Time

// 不可导出别名
type t = time.Time

Although both type aliases point to the same underlying typetime .Time, but their performance is different.

The following benchmark demonstrates this difference:

import (
    "testing"
    "time"
)

func BenchmarkT(b *testing.B) {
    var t T
    for i := 0; i < b.N; i++ {
        t = t.Add(1)
    }
}

func Benchmarkt(b *testing.B) {
    var t t
    for i := 0; i < b.N; i++ {
        t = t.Add(1)
    }
}

Running the benchmark will show that Benchmarkt is significantly faster than BenchmarkT. This is because non-exportable aliases do not generate pointers, thus avoiding the overhead of pointer dereferences.

Conclusion

In Golang performance optimization, it is important to choose type aliases carefully. Using non-exportable aliases improves performance by avoiding the additional overhead of pointer dereferences and stack allocations. However, if the alias type needs to be accessible from outside the package, you must use an exportable alias. Therefore, carefully weighing the pros and cons of these two class names is crucial to improving code execution efficiency.

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