Performance

Zero-Cost Abstraction

Phantom types exist only in the type system. At runtime, ID[UserBrand, string] is just a struct wrapping a string. The compiler eliminates the brand type entirely.

Benchmark Results

Benchmarked on Go 1.26.4 with GOEXPERIMENT=jsonv2:

Operation	Latency	Allocations
NewID	~0.4 ns	0
Get	~1 ns	0
Equal	~0.3 ns	0
Compare	~3 ns	0
IsZero	~1.4 ns	0
String (no brand)	~5 ns	0
String (named)	~30 ns	1
MarshalJSON	~200 ns	3
MarshalBinary	~22 ns	1
Scan (string)	~44 ns	1

Core operations (NewID, Get, Equal, Compare, IsZero) and unbranded String() are zero-allocation.

Named-brand String() requires one allocation for the "Brand:value" concatenation.

Reproducing

GOEXPERIMENT=jsonv2 go test -bench=. -benchmem ./...

Why So Fast

• No reflection — all type handling is via type switches at known boundaries
• No boxing — the underlying value is stored directly
• No indirection — brand types are zero-size, eliminated by the compiler
• Direct writes — Format() writes directly to io.Writer instead of allocating strings (v0.3.1+)

Format Optimization

Since v0.3.1, Format() (used by fmt.Sprintf, fmt.Printf, etc.) writes directly to the fmt.State’s writer instead of allocating an intermediate string. This means %s and %v formatting of IDs avoids allocations for unnamed brands.