goType errorEasy

Value receiver fails to mutate struct state

Time: 0:00

BugFind the bug and fix the code

What it should do

Add an amount to a metric accumulator and return the updated total. Example: accumulateMetrics(10, 5) -> 15

What happens instead

Accumulator returns 10 instead of 15 because updates are discarded

package main

import "fmt"

type Metric struct {
	Total int
}

func (m Metric) Add(val int) {
	m.Total += val
}

func accumulateMetrics(initial int, delta int) int {
	m := Metric{Total: initial}
	m.Add(delta)
	return m.Total
}

func main() {
	fmt.Println(accumulateMetrics(10, 5))
}

Test a custom input to verify an edge case (e.g. empty lists, negative numbers, duplicates).

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This bug belongs to the type errors pattern

Totals that concatenate, sorts that put 10 before 9, comparisons that refuse to run.

Learn the type errors pattern Step through your own code

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package main import "fmt" type Metric struct { Total int } func (m Metric) Add(val int) { m.Total += val } func accumulateMetrics(initial int, delta int) int { m := Metric{Total: initial} m.Add(delta) return m.Total } func main() { fmt.Println(accumulateMetrics(10, 5)) }

Value receiver fails to mutate struct state

What it should do

What happens instead

More type errors to practise

Value receiver fails to mutate struct state

What it should do

What happens instead

More type errors to practise