How does Go embody the Interface Segregation Principle (ISP)?

The Interface Segregation Principle states: clients should not be forced to depend on methods they do not use. Go's implicit, structural interfaces make ISP trivially achievable — any consumer can define the minimal interface it needs, independently of what the concrete type exposes.

// A concrete type with many methods (a real storage backend)
type RedisClient struct{ pool *redis.Pool }
func (r *RedisClient) Get(key string) (string, error)        { /* ... */ return "", nil }
func (r *RedisClient) Set(key, val string, ttl time.Duration) error { /* ... */ return nil }
func (r *RedisClient) Delete(key string) error               { /* ... */ return nil }
func (r *RedisClient) Increment(key string) (int64, error)   { /* ... */ return 0, nil }
func (r *RedisClient) Expire(key string, d time.Duration) error { /* ... */ return nil }
func (r *RedisClient) Ping() error                           { /* ... */ return nil }

// Package: cache — only needs Get and Set
type Getter interface{ Get(key string) (string, error) }
type Setter interface{ Set(key, val string, ttl time.Duration) error }
type Cache interface { Getter; Setter }   // composed

func newCacheLayer(c Cache) *CacheLayer { return &CacheLayer{c: c} }

// Package: rate-limiter — only needs Increment and Expire
type Counter interface {
    Increment(key string) (int64, error)
    Expire(key string, d time.Duration) error
}
func newRateLimiter(c Counter) *RateLimiter { return &RateLimiter{c: c} }

// Package: health — only needs Ping
type Pinger interface{ Ping() error }
func newHealthCheck(p Pinger) *HealthCheck { return &HealthCheck{p: p} }

// RedisClient satisfies ALL of Cache, Counter, and Pinger
redis := &RedisClient{pool: pool}
cache   := newCacheLayer(redis)    // passes as Cache
limiter := newRateLimiter(redis)   // passes as Counter
health  := newHealthCheck(redis)   // passes as Pinger

Each consumer defines its own minimal interface — without RedisClient knowing about any of them. Adding a new consumer with a new subset of methods requires zero changes to RedisClient. This is ISP at its most natural: Go's structural typing makes it the path of least resistance.

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