add custom getter and setter functions

tests/get_set.rs

@@ -0,0 +1,54 @@
+use std::{cell::Cell, str::from_utf8};
+
+use macroconf::config;
+use miniconf::JsonCoreSlash;
+
+fn set_cell<const MIN: i32, const MAX: i32>(
+    cell: &Cell<i32>,
+    val: i32,
+) -> Result<(), &'static str> {
+    if (MIN..=MAX).contains(&val) {
+        cell.set(val);
+        Ok(())
+    } else {
+        Err("value out of bounds")
+    }
+}
+
+#[config]
+struct Config {
+    #[config(
+        min = "-128",
+        max = "128",
+        default,
+        typ = "i32",
+        get = "Cell::get",
+        set = "set_cell::<-128,128>"
+    )]
+    field: Cell<i32>,
+}
+
+#[test]
+fn get() {
+    let mut buffer = [0u8; 32];
+    let config = Config {
+        field: __ConfigField::new(Cell::new(42)),
+    };
+    let len = config.get_json("/field", &mut buffer).unwrap();
+    assert_eq!(from_utf8(&buffer[..len]), Ok("42"));
+}
+
+#[test]
+fn set() {
+    let mut config = Config {
+        field: __ConfigField::new(Cell::new(42)),
+    };
+    config.set_json("/field", b"-32").unwrap();
+    assert_eq!(config.field.get(), -32);
+    config
+        .set_json("/field", b"256")
+        .expect_err("result not checked");
+    config
+        .set_json("/field", b"-256")
+        .expect_err("result not checked");
+}