doc: libevm/pseudo package comments and improved readability

libevm/pseudo/type.go

@@ -1,4 +1,15 @@
-// Package pseudo ...
+// Package pseudo provides a bridge between generic and non-generic code via
+// pseudo-types and pseudo-values. With careful usage, there is minimal
+// reduction in type safety.
+//
+// Adding generic type parameters to anything (e.g. struct, function, etc)
+// "pollutes" all code that uses the generic type. Refactoring all uses isn't
+// always feasible, and a [Type] acts as an intermediate fix. Although their
+// constructors are generic, they are not, and they are instead coupled with a
+// generic [Value] that SHOULD be used for access.
+//
+// Packages typically SHOULD NOT expose a [Type] and SHOULD instead provide
+// users with a type-safe [Value].
 package pseudo
 
 import (
@@ -6,63 +17,101 @@ import (
 	"fmt"
 )
 
-// Zero ...
+// A Type wraps a strongly-typed value without exposing information about its
-func Zero[T any]() (*Type, *Value[T]) {
+// type. It can be used in lieu of a generic field / parameter.
-	var x T
-	return From[T](x)
-}
-
-// From ...
-func From[T any](x T) (*Type, *Value[T]) {
-	t := &Type{
-		val: &concrete[T]{
-			val: x,
-		},
-	}
-	return t, NewValueUnsafe[T](t)
-}
-
-// OnlyType ...
-func OnlyType[T any](t *Type, _ *Value[T]) *Type {
-	return t
-}
-
-// A Type ...
 type Type struct {
 	val value
 }
 
-func (t *Type) Interface() any { return t.val.get() }
+// A Value provides strongly-typed access to the payload carried by a [Type].
-
-// func (t *Type) Set(v any) error              { return t.val.Set(v) }
-// func (t *Type) MustSet(v any)                { t.val.MustSet(v) }
-func (t *Type) MarshalJSON() ([]byte, error) { return t.val.MarshalJSON() }
-func (t *Type) UnmarshalJSON(b []byte) error { return t.val.UnmarshalJSON(b) }
-
-var (
-	_ json.Marshaler   = (*Type)(nil)
-	_ json.Unmarshaler = (*Type)(nil)
-)
-
-func NewValueUnsafe[T any](t *Type) *Value[T] {
-	return &Value[T]{t: t}
-}
-
-func NewValue[T any](t *Type) (*Value[T], error) {
-	var x T
-	if !t.val.canSetTo(x) {
-		return nil, fmt.Errorf("cannot create *Accessor[%T] with *Type carrying %T", x, t.val.get())
-	}
-	return NewValueUnsafe[T](t), nil
-}
-
 type Value[T any] struct {
 	t *Type
 }
 
-func (a *Value[T]) Get() T  { return a.t.val.get().(T) }
+// A Pseudo type couples a [Type] and a [Value]. If returned by a constructor
+// from this package, both wrap the same payload.
+type Pseudo[T any] struct {
+	Type  *Type
+	Value *Value[T]
+}
+
+// TypeAndValue is a convenience function for splitting the contents of `p`,
+// typically at construction.
+func (p *Pseudo[T]) TypeAndValue() (*Type, *Value[T]) {
+	return p.Type, p.Value
+}
+
+// From returns a Pseudo[T] constructed from `v`.
+func From[T any](v T) *Pseudo[T] {
+	t := &Type{
+		val: &concrete[T]{
+			val: v,
+		},
+	}
+	return &Pseudo[T]{t, MustNewValue[T](t)}
+}
+
+// Zero is equivalent to [From] called with the [zero value] of type `T`. Note
+// that pointers, slices, maps, etc. will therefore be nil.
+//
+// [zero value]: https://go.dev/tour/basics/12
+func Zero[T any]() *Pseudo[T] {
+	var x T
+	return From[T](x)
+}
+
+// Interface returns the wrapped value as an `any`, equivalent to
+// [reflect.Value.Interface]. Prefer [Value.Get].
+func (t *Type) Interface() any { return t.val.get() }
+
+// NewValue constructs a [Value] from a [Type], first confirming that `t` wraps
+// a payload of type `T`.
+func NewValue[T any](t *Type) (*Value[T], error) {
+	var x T
+	if !t.val.canSetTo(x) {
+		return nil, fmt.Errorf("cannot create *Value[%T] with *Type carrying %T", x, t.val.get())
+	}
+	return &Value[T]{t}, nil
+}
+
+// MustNewValue is equivalent to [NewValue] except that it panics instead of
+// returning an error.
+func MustNewValue[T any](t *Type) *Value[T] {
+	v, err := NewValue[T](t)
+	if err != nil {
+		panic(err)
+	}
+	return v
+}
+
+// Get returns the value.
+func (a *Value[T]) Get() T { return a.t.val.get().(T) }
+
+// Set sets the value.
 func (a *Value[T]) Set(v T) { a.t.val.mustSet(v) }
 
+// MarshalJSON implements the [json.Marshaler] interface.
+func (t *Type) MarshalJSON() ([]byte, error) { return t.val.MarshalJSON() }
+
+// UnmarshalJSON implements the [json.Unmarshaler] interface.
+func (t *Type) UnmarshalJSON(b []byte) error { return t.val.UnmarshalJSON(b) }
+
+// MarshalJSON implements the [json.Marshaler] interface.
+func (v *Value[T]) MarshalJSON() ([]byte, error) { return v.t.MarshalJSON() }
+
+// UnmarshalJSON implements the [json.Unmarshaler] interface.
+func (v *Value[T]) UnmarshalJSON(b []byte) error { return v.t.UnmarshalJSON(b) }
+
+var _ = []interface {
+	json.Marshaler
+	json.Unmarshaler
+}{
+	(*Type)(nil),
+	(*Value[struct{}])(nil),
+	(*concrete[struct{}])(nil),
+}
+
+// A value is a non-generic wrapper around a [concrete] struct.
 type value interface {
 	get() any
 	canSetTo(any) bool
@@ -84,11 +133,14 @@ func (c *concrete[T]) canSetTo(v any) bool {
 	return ok
 }
 
-type InvalidTypeError[T any] struct {
+// An invalidTypeError is returned by [conrete.set] if the value is incompatible
+// with its type. This should never leave this package and exists only to
+// provide precise testing of unhappy paths.
+type invalidTypeError[T any] struct {
 	SetTo any
 }
 
-func (e *InvalidTypeError[T]) Error() string {
+func (e *invalidTypeError[T]) Error() string {
 	var t T
 	return fmt.Sprintf("cannot set %T to %T", t, e.SetTo)
 }
@@ -96,7 +148,9 @@ func (e *InvalidTypeError[T]) Error() string {
 func (c *concrete[T]) set(v any) error {
 	vv, ok := v.(T)
 	if !ok {
-		return &InvalidTypeError[T]{SetTo: v}
+		// Other invariants in this implementation (aim to) guarantee that this
+		// will never happen.
+		return &invalidTypeError[T]{SetTo: v}
 	}
 	c.val = vv
 	return nil

libevm/pseudo/type_test.go

@@ -15,7 +15,7 @@ func TestType(t *testing.T) {
 
 	testType(
 		t, "From[uint](314159)",
-		func() (*Type, *Value[uint]) {
+		func() *Pseudo[uint] {
 			return From[uint](314159)
 		},
 		314159, 0, struct{}{},
@@ -24,20 +24,20 @@ func TestType(t *testing.T) {
 	testType(t, "nil pointer", Zero[*float64], (*float64)(nil), new(float64), 0)
 }
 
-func testType[T any](t *testing.T, name string, ctor func() (*Type, *Value[T]), init T, setTo T, invalid any) {
+func testType[T any](t *testing.T, name string, ctor func() *Pseudo[T], init T, setTo T, invalid any) {
 	t.Run(name, func(t *testing.T) {
-		typ, val := ctor()
+		typ, val := ctor().TypeAndValue()
 		assert.Equal(t, init, val.Get())
 		val.Set(setTo)
 		assert.Equal(t, setTo, val.Get())
 
 		t.Run("set to invalid type", func(t *testing.T) {
-			wantErr := &InvalidTypeError[T]{SetTo: invalid}
+			wantErr := &invalidTypeError[T]{SetTo: invalid}
 
 			assertError := func(t *testing.T, err any) {
 				t.Helper()
 				switch err := err.(type) {
-				case *InvalidTypeError[T]:
+				case *invalidTypeError[T]:
 					assert.Equal(t, wantErr, err)
 				default:
 					t.Errorf("got error %v; want %v", err, wantErr)
@@ -60,9 +60,20 @@ func testType[T any](t *testing.T, name string, ctor func() (*Type, *Value[T]),
 			buf, err := json.Marshal(typ)
 			require.NoError(t, err)
 
-			got, gotVal := Zero[T]()
+			got, gotVal := Zero[T]().TypeAndValue()
 			require.NoError(t, json.Unmarshal(buf, &got))
 			assert.Equal(t, val.Get(), gotVal.Get())
 		})
 	})
 }
+
+func ExamplePseudo_TypeAndValue() {
+	typ, val := From("hello").TypeAndValue()
+
+	// But, if only one is needed:
+	typ = From("world").Type
+	val = From("this isn't coupled to the Type").Value
+
+	_ = typ
+	_ = val
+}

params/config.libevm.go

@@ -56,12 +56,12 @@ type ExtraPayloadGetter[C any, R any] struct{}
 
 // FromChainConfig ...
 func (ExtraPayloadGetter[C, R]) FromChainConfig(c *ChainConfig) *C {
-	return pseudo.NewValueUnsafe[*C](c.extraPayload()).Get()
+	return pseudo.MustNewValue[*C](c.extraPayload()).Get()
 }
 
 // FromRules ...
 func (ExtraPayloadGetter[C, R]) FromRules(r *Rules) *R {
-	return pseudo.NewValueUnsafe[*R](r.extraPayload()).Get()
+	return pseudo.MustNewValue[*R](r.extraPayload()).Get()
 }
 
 func mustBeStruct[T any]() {
@@ -160,19 +160,17 @@ func (r *Rules) extraPayload() *pseudo.Type {
 	return r.extra
 }
 
-func (Extras[C, R]) nilForChainConfig() *pseudo.Type { return pseudo.OnlyType(pseudo.Zero[*C]()) }
+func (Extras[C, R]) nilForChainConfig() *pseudo.Type { return pseudo.Zero[*C]().Type }
-func (Extras[C, R]) nilForRules() *pseudo.Type       { return pseudo.OnlyType(pseudo.Zero[*R]()) }
+func (Extras[C, R]) nilForRules() *pseudo.Type       { return pseudo.Zero[*R]().Type }
 
 func (*Extras[C, R]) newForChainConfig() *pseudo.Type {
 	var x C
-	return pseudo.OnlyType(pseudo.From(&x))
+	return pseudo.From(&x).Type
 }
 
 func (e *Extras[C, R]) newForRules(c *ChainConfig, r *Rules, blockNum *big.Int, isMerge bool, timestamp uint64) *pseudo.Type {
 	if e.NewForRules == nil {
 		return e.nilForRules()
 	}
-	return pseudo.OnlyType(
+	return pseudo.From(e.NewForRules(c, r, c.extra.Interface().(*C), blockNum, isMerge, timestamp)).Type
-		pseudo.From(e.NewForRules(c, r, c.extra.Interface().(*C), blockNum, isMerge, timestamp)),
-	)
 }

params/config.libevm_test.go

@@ -56,9 +56,9 @@ func TestRegisterExtras(t *testing.T) {
 					},
 				})
 			},
-			ccExtra: pseudo.OnlyType(pseudo.From(&ccExtraA{
+			ccExtra: pseudo.From(&ccExtraA{
 				A: "hello",
-			})),
+			}).Type,
 			wantRulesExtra: &rulesExtraA{
 				A: "hello",
 			},
@@ -68,9 +68,9 @@ func TestRegisterExtras(t *testing.T) {
 			register: func() {
 				RegisterExtras(Extras[ccExtraB, rulesExtraB]{})
 			},
-			ccExtra: pseudo.OnlyType(pseudo.From(&ccExtraB{
+			ccExtra: pseudo.From(&ccExtraB{
 				B: "world",
-			})),
+			}).Type,
 			wantRulesExtra: (*rulesExtraB)(nil),
 		},
 		{
@@ -78,9 +78,9 @@ func TestRegisterExtras(t *testing.T) {
 			register: func() {
 				RegisterExtras(Extras[rawJSON, struct{}]{})
 			},
-			ccExtra: pseudo.OnlyType(pseudo.From(&rawJSON{
+			ccExtra: pseudo.From(&rawJSON{
 				RawMessage: []byte(`"hello, world"`),
-			})),
+			}).Type,
 			wantRulesExtra: (*struct{})(nil),
 		},
 	}