Add ExecuteData::get_mut_parameter method. (#108)

Author: jmjoy

phper/src/values.rs

@@ -161,7 +161,15 @@ impl ExecuteData {
     }
 
     /// Gets parameter by index.
-    pub fn get_parameter(&mut self, index: usize) -> &mut ZVal {
+    pub fn get_parameter(&self, index: usize) -> &ZVal {
+        unsafe {
+            let val = phper_zend_call_var_num(self.as_ptr() as *mut _, index.try_into().unwrap());
+            ZVal::from_ptr(val)
+        }
+    }
+
+    /// Gets mutable parameter by index.
+    pub fn get_mut_parameter(&mut self, index: usize) -> &mut ZVal {
         unsafe {
             let val = phper_zend_call_var_num(self.as_mut_ptr(), index.try_into().unwrap());
             ZVal::from_mut_ptr(val)