String.prototype.at (and autoformatting)

valuescript_vm/src/string_methods.rs

@@ -0,0 +1,30 @@
+use std::rc::Rc;
+
+use crate::{helpers::to_wrapping_index, native_function::NativeFunction, vs_value::Val};
+
+pub fn get_string_method(method: &str) -> Val {
+  match method {
+    "at" => Val::Static(&AT),
+    _ => Val::Undefined,
+  }
+}
+
+static AT: NativeFunction = NativeFunction {
+  fn_: |this: &mut Val, params: Vec<Val>| -> Val {
+    match this {
+      Val::String(string_data) => {
+        let string_bytes = string_data.as_bytes();
+
+        let index = match to_wrapping_index(params.get(0), string_bytes.len()) {
+          None => return Val::Undefined,
+          Some(i) => i,
+        };
+
+        let byte = string_bytes[index];
+
+        Val::String(Rc::new(String::from_utf8_lossy(&[byte]).into_owned()))
+      }
+      _ => std::panic!("Not implemented: exceptions/string indirection"),
+    }
+  },
+};