From 097d3a0e6cc5dd3074753fb140e392214f61c4d0 Mon Sep 17 00:00:00 2001
From: Yuya Nishihara <yuya@tcha.org>
Date: Sun, 5 Feb 2023 19:35:34 +0900
Subject: [PATCH] templater: add generic wrappers for Option<TemplateProperty>

Option<P> allows us to embed optional argument property in tuple.

    let maybe_arg = maybe_pair.map(|pair| parse(...))?;
    chain_properties((self, maybe_arg), |_: &(Context, Option<_>)| ...)

For one optional argument, we can instead switch the property functions:

    if let Some(pair) = maybe_pair {
        let arg = pair.map(|pair| parse(...))?;
        chain_properties((self, arg), |_: &(Context, _)| ...)
    } else {
        chain_properties(self, |_: &Context| ...)
    }

If we have various combinations of optional arguments, using Option<P> would
be better.
---
 src/templater.rs | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/templater.rs b/src/templater.rs
index e965ed2e7..a83aa66ce 100644
--- a/src/templater.rs
+++ b/src/templater.rs
@@ -210,6 +210,14 @@ impl<C, P: TemplateProperty<C> + ?Sized> TemplateProperty<C> for Box<P> {
     }
 }
 
+impl<C, P: TemplateProperty<C>> TemplateProperty<C> for Option<P> {
+    type Output = Option<P::Output>;
+
+    fn extract(&self, context: &C) -> Self::Output {
+        self.as_ref().map(|property| property.extract(context))
+    }
+}
+
 // Implement TemplateProperty for tuples
 macro_rules! tuple_impls {
     ($( ( $($n:tt $T:ident),+ ) )+) => {