Why Do I Get 'Invalid Operation - Type *map[key]value Does Not Support Indexing' in Go?

Go: Invalid Operation - Type *map[key]value Does Not Support Indexing

In Go, attempts to pass a map by pointer and modify the original map through the pointer may result in an "invalid operation" error. This is because indexing on a pointer to a map is not supported in Go.

To resolve this issue, it is necessary to index on the map itself rather than the pointer. Here's a modified code that demonstrates how to do this:

package main

import "fmt"

type Currency string

type Amount struct {
    Currency Currency
    Value float32
}

type Balance map[Currency]float32

func (b *Balance) Add(amount Amount) *Balance {
    current, ok := (*b)[amount.Currency]
    if ok {
        (*b)[amount.Currency] = current + amount.Value
    } else {
        (*b)[amount.Currency] = amount.Value
    }
    return b
}

func main() {
    b := &Balance{Currency("USD"): 100.0}
    b = b.Add(Amount{Currency: Currency("USD"), Value: 5.0})

    fmt.Println("Balance: ", (*b))
}

By dereferencing the pointer to the map (*b) before indexing, the code now correctly modifies the original map.

Note: While the above code demonstrates how to modify a map through a pointer, it is generally more idiomatic to pass the map by value in Go. By passing a value, changes made to the map are automatically propagated back to the original map.

The above is the detailed content of Why Do I Get 'Invalid Operation - Type *map[key]value Does Not Support Indexing' in Go?. For more information, please follow other related articles on the PHP Chinese website!