Value receiver

Learn read-only methods with a value receiver.

Value receivers

A value receiver means the method works on a copy of the receiver; the method can't change it. This is a clear guarantee for read-only computations:

type Para struct{ Kurus int64 }

func (p Para) String() string {
    return fmt.Sprintf("%d,%02d TL", p.Kurus/100, p.Kurus%100)
}

func (p Para) Ekle(q Para) Para {
    return Para{p.Kurus + q.Kurus}  // returns a new value
}

Immutable value types

time.Time in the standard library is an example of this approach: t.Add(time.Hour) doesn't change t but returns a new time. Immutable types can be shared safely in concurrent code and are less error-prone. A value receiver can also be called through both a value and a pointer: (&p).String() works too.

Exercise Money type

Write the Para type above with its String() and Ekle methods. For a := Para{1250} and b := a.Ekle(Para{375}), print a and b (String() is used).

Show example solution

package main

import "fmt"

type Para struct{ Kurus int64 }

func (p Para) String() string {
    return fmt.Sprintf("%d,%02d TL", p.Kurus/100, p.Kurus%100)
}

func (p Para) Ekle(q Para) Para {
    return Para{p.Kurus + q.Kurus}
}

func main() {
    a := Para{1250}
    b := a.Ekle(Para{375})
    fmt.Println(a, b)
}

Test yourself

After <code>a := Para{150}; b := a.Ekle(Para{50})</code>, what is <code>a.Kurus</code>?
- 200
- 50
- 0
- 150
Show answer

150 — Ekle has a value receiver and returns a new Para; a stays the same and b becomes 200.

Return a new value

func (p Para) Ekle(q Para) Para {
    ____ Para{p.Kurus + q.Kurus}
}

Show answer

func (p Para) Ekle(q Para) Para {
    return Para{p.Kurus + q.Kurus}
}

Receiver kind and property

Value receiver

Works on a copy
Pointer receiver

Changes the original
time.Time.Add

Returns a new value
String() string

Print format

Next lesson: Methods and embedding

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