Add VTableBuilder

Experimenting with using a builder instead of a macro for making vtables.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/obj/mod.rs

@@ -14,9 +14,10 @@ pub mod prelude {
     pub use crate::obj::int::*;
     pub use crate::obj::quote::*;
     pub use crate::obj::str::*;
-    pub use crate::obj::{Obj, ObjPtr, VTable};
+    pub use crate::obj::{Obj, ObjPtr, VTable, VTableBuilder};
 }
 
+use crate::obj::builtin::{BuiltinFn, BuiltinFnObj, BuiltinFnPtr};
 use crate::syn::span::Span;
 use crate::vm::{error::*, machine::Machine};
 use gc::{Finalize, Gc, Trace};
@@ -27,6 +28,28 @@ use std::fmt::Debug;
 pub type ObjPtr = Gc<dyn Obj + 'static>;
 pub type VTable = HashMap<String, ObjPtr>;
 
+#[derive(Debug, Clone, Default)]
+pub struct VTableBuilder {
+    vtable: VTable,
+}
+
+impl VTableBuilder {
+    pub fn with(mut self, name: impl ToString, obj: ObjPtr) -> Self {
+        self.vtable.insert(name.to_string(), obj);
+        self
+    }
+
+    pub fn with_builtin(self, name: impl ToString, fun: BuiltinFnPtr) -> Self {
+        let name = name.to_string();
+        let fun = BuiltinFnObj::new(BuiltinFn::new(name.clone(), fun));
+        self.with(name, fun)
+    }
+
+    pub fn finish(self) -> VTable {
+        self.vtable
+    }
+}
+
 /// An object that has a vtable and common functions.
 pub trait Obj: Trace + Finalize + Debug {
     /// Gets the vtable for this object.