libgo/go/go/parser/testdata/metrics.go2

package metrics

import "sync"

type Metric1[T comparable] struct {
	mu sync.Mutex
	m  map[T]int
}

func (m *Metric1[T]) Add(v T) {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.m == nil {
		m.m = make(map[T]int)
	}
	m[v]++
}

type key2[T1, T2 comparable] struct {
	f1 T1
	f2 T2
}

type Metric2[T1, T2 cmp2] struct {
	mu sync.Mutex
	m  map[key2[T1, T2]]int
}

func (m *Metric2[T1, T2]) Add(v1 T1, v2 T2) {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.m == nil {
		m.m = make(map[key2[T1, T2]]int)
	}
	m[key[T1, T2]{v1, v2}]++
}

type key3[T1, T2, T3 comparable] struct {
	f1 T1
	f2 T2
	f3 T3
}

type Metric3[T1, T2, T3 comparable] struct {
	mu sync.Mutex
	m  map[key3[T1, T2, T3]]int
}

func (m *Metric3[T1, T2, T3]) Add(v1 T1, v2 T2, v3 T3) {
	m.mu.Lock()
	defer m.mu.Unlock()
	if m.m == nil {
		m.m = make(map[key3]int)
	}
	m[key[T1, T2, T3]{v1, v2, v3}]++
}

// Repeat for the maximum number of permitted arguments.