Remove explicit S type parameters (#5275)

* Remove explicit `S` type parameters

This commit removes the explicit `S` type parameter on `Func::typed` and
`Instance::get_typed_func`. Historical versions of Rust required that
this be a type parameter but recent rustcs support a mixture of explicit
type parameters and `impl Trait`. This removes, at callsites, a
superfluous `, _` argument which otherwise never needs specification.

* Fix mdbook examples

docs/lang-rust.md

@@ -86,7 +86,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     // There's a few ways we can call the `answer` `Func` value. The easiest
     // is to statically assert its signature with `typed` (in this case
     // asserting it takes no arguments and returns one i32) and then call it.
-    let answer = answer.typed::<(), i32, _>(&store)?;
+    let answer = answer.typed::<(), i32>(&store)?;
 
     // And finally we can call our function! Note that the error propagation
     // with `?` is done to handle the case where the wasm function traps.
@@ -184,7 +184,7 @@ fn main() -> Result<(), Box<dyn Error>> {
     let instance = linker.instantiate(&mut store, &module)?;
 
     // Like before, we can get the run function and execute it.
-    let run = instance.get_typed_func::<(), (), _>(&mut store, "run")?;
+    let run = instance.get_typed_func::<(), ()>(&mut store, "run")?;
     run.call(&mut store, ())?;
 
     // We can also inspect what integers were logged:

docs/wasm-wat.md

@@ -47,7 +47,7 @@ let wat = r#"
 "#;
 let module = Module::new(store.engine(), wat)?;
 let instance = Instance::new(&mut store, &module, &[])?;
-let add = instance.get_typed_func::<(i32, i32), i32, _>(&mut store, "add")?;
+let add = instance.get_typed_func::<(i32, i32), i32>(&mut store, "add")?;
 println!("1 + 2 = {}", add.call(&mut store, (1, 2))?);
 # Ok(())
 # }