How to iterate over string fields in a struct using reflection in Go?

Iterating Over String Fields in a Struct

Problem:

Iterating over the string fields of a struct presents a challenge, especially when seeking to perform cleanup or validation operations. Implementing this with a switch-case approach lacks scalability and is unsuitable when leveraging the gorilla/schema for unmarshalling.

Solution:

Reflect provides an avenue for iterating over struct fields and manipulating string fields seamlessly. Here's how it can be achieved:

1. Obtain a Pointer to the Struct:
   To modify values, a pointer to the struct is required.
2. Iterate Over Fields:
   Use NumFields() to determine the number of fields and Field() to iterate over each field in the struct.
3. Check Field Type:
   Verify each field's type using Type(). Only string fields require modification.
4. Clean Up String:
   Retrieve the field's value with Interface() and apply desired cleanup operations from the strings package (e.g., TrimSpace).
5. Update Value:
   Use SetString() to update the value of the string field.

Example:

<code class="go">package main

import (
    "fmt"
    "reflect"
    "strings"
)

type MyStruct struct {
    A, B, C string
    I int
    D string
    J int
}

func main() {
    ms := MyStruct{"Green ", "Eggs", " and ", 2, "Ham      ", 15}
    fmt.Printf("%s%s%s%d%s%d\n", ms.A, ms.B, ms.C, ms.I, ms.D, ms.J)

    msValuePtr := reflect.ValueOf(&ms)
    msValue := msValuePtr.Elem()

    for i := 0; i < msValue.NumField(); i++ {
        field := msValue.Field(i)
        if field.Type() != reflect.TypeOf("") {
            continue
        }
        str := field.Interface().(string)
        str = strings.TrimSpace(str)
        field.SetString(str)
    }
    fmt.Printf("%s%s%s%d%s%d\n", ms.A, ms.B, ms.C, ms.I, ms.D, ms.J)
}</code>

Caveats:

• This approach requires a pointer to the struct.
• Reflect may panic when trying to modify unexported fields. Handle this by implementing the code within the package.

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