start to support skip serializing if feature

issue #43

yaserde/tests/se_namespace.rs

@@ -183,7 +183,7 @@ fn ser_struct_default_namespace_via_attribute() {
 }
 
 #[test]
-fn de_struct_namespace_nested() {
+fn ser_struct_namespace_nested() {
   #[derive(YaSerialize, Default, PartialEq, Debug)]
   #[yaserde(prefix = "nsa", namespace = "nsa: http://www.sample.com/ns/a")]
   struct A {

yaserde/tests/ser_skip.rs

@@ -0,0 +1,68 @@
+extern crate log;
+extern crate xml;
+extern crate yaserde;
+#[macro_use]
+extern crate yaserde_derive;
+
+use std::io::Write;
+use yaserde::ser::to_string;
+use yaserde::YaSerialize;
+
+macro_rules! convert_and_validate {
+  ($model: expr, $content: expr) => {
+    let data: Result<String, String> = to_string(&$model);
+    assert_eq!(
+      data,
+      Ok(
+        String::from($content)
+          .split("\n")
+          .map(|s| s.trim())
+          .collect::<String>()
+      )
+    );
+  };
+}
+
+#[test]
+fn ser_skip_serializing_if_for_struct() {
+  #[derive(YaSerialize, PartialEq, Debug)]
+  #[yaserde(root = "base")]
+  pub struct XmlStruct {
+    #[yaserde(skip_serializing_if = "check_string_function")]
+    string_item: String,
+    #[yaserde(skip_serializing_if = "check_bool_function")]
+    bool_item: bool,
+    #[yaserde(skip_serializing_if = "check_f32_function")]
+    f32_item: f32,
+    #[yaserde(skip_serializing_if = "check_option_string_function")]
+    option_string_item: Option<String>,
+  }
+
+  impl XmlStruct {
+    fn check_string_function(&self, value: &String) -> bool {
+      value == "something"
+    }
+
+    fn check_option_string_function(&self, value: &Option<String>) -> bool {
+      value == &Some("something".to_string())
+    }
+
+    fn check_bool_function(&self, value: &bool) -> bool {
+      value == &true
+    }
+
+    fn check_f32_function(&self, value: &f32) -> bool {
+      value == &0.0
+    }
+  }
+
+  let model = XmlStruct {
+    string_item: "something".to_string(),
+    bool_item: true,
+    f32_item: 0.0,
+    option_string_item: Some("something".to_string()),
+  };
+
+  let content = "<?xml version=\"1.0\" encoding=\"utf-8\"?><base />";
+  convert_and_validate!(model, content);
+}