From cc36bed00059f817c988e352ebda3bd1d4d86606 Mon Sep 17 00:00:00 2001
From: Arran Schlosberg <me@arranschlosberg.com>
Date: Wed, 11 Sep 2024 17:12:54 +0100
Subject: [PATCH] feat: `pseudo.PointerTo()`

---
 libevm/pseudo/type.go      | 21 +++++++++++++++++++++
 libevm/pseudo/type_test.go | 23 +++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/libevm/pseudo/type.go b/libevm/pseudo/type.go
index 8c453f4cb0e7..8d1568638ed5 100644
--- a/libevm/pseudo/type.go
+++ b/libevm/pseudo/type.go
@@ -60,6 +60,27 @@ func Zero[T any]() *Pseudo[T] {
 	return From[T](x)
 }
 
+// PointerTo is equivalent to [From] called with a pointer to the payload
+// carried by `t`. It first confirms that the payload is of type `T`.
+func PointerTo[T any](t *Type) (*Pseudo[*T], error) {
+	c, ok := t.val.(*concrete[T])
+	if !ok {
+		var want *T
+		return nil, fmt.Errorf("cannot create *Pseudo[%T] from *Type carrying %T", want, t.val.get())
+	}
+	return From(&c.val), nil
+}
+
+// MustPointerTo is equivalent to [PointerTo] except that it panics instead of
+// returning an error.
+func MustPointerTo[T any](t *Type) *Pseudo[*T] {
+	p, err := PointerTo[T](t)
+	if err != nil {
+		panic(err)
+	}
+	return p
+}
+
 // 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() }
diff --git a/libevm/pseudo/type_test.go b/libevm/pseudo/type_test.go
index 27ecf7e497ea..0b25c945ce29 100644
--- a/libevm/pseudo/type_test.go
+++ b/libevm/pseudo/type_test.go
@@ -77,3 +77,26 @@ func ExamplePseudo_TypeAndValue() {
 	_ = typ
 	_ = val
 }
+
+func TestPointer(t *testing.T) {
+	type carrier struct {
+		payload int
+	}
+
+	typ, val := From(carrier{42}).TypeAndValue()
+
+	t.Run("invalid type", func(t *testing.T) {
+		_, err := PointerTo[int](typ)
+		require.Errorf(t, err, "PointerTo[int](%T)", carrier{})
+	})
+
+	t.Run("valid type", func(t *testing.T) {
+		ptrVal := MustPointerTo[carrier](typ).Value
+
+		assert.Equal(t, 42, val.Get().payload, "before setting via pointer")
+		var ptr *carrier = ptrVal.Get()
+		ptr.payload = 314159
+		assert.Equal(t, 314159, val.Get().payload, "after setting via pointer")
+	})
+
+}