From 0d118ef0c95d5b2ba306372c97526cd2aaaac679 Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Mon, 26 Nov 2018 19:57:20 +0100
Subject: [PATCH] Bindings::get(): Add convenience method

This allows writing attribute lookups as

    if (auto name = value.attrs->get(state.sName))
      ...

(cherry picked from commit f216c76c56cdffb5214d074a7d44812843dd174f)
---
 src/libexpr/attr-set.hh | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/libexpr/attr-set.hh b/src/libexpr/attr-set.hh
index 3119a1848..6c5fb21ad 100644
--- a/src/libexpr/attr-set.hh
+++ b/src/libexpr/attr-set.hh
@@ -4,6 +4,7 @@
 #include "symbol-table.hh"
 
 #include <algorithm>
+#include <optional>
 
 namespace nix {
 
@@ -63,6 +64,14 @@ public:
         return end();
     }
 
+    std::optional<Attr *> get(const Symbol & name)
+    {
+        Attr key(name, 0);
+        iterator i = std::lower_bound(begin(), end(), key);
+        if (i != end() && i->name == name) return &*i;
+        return {};
+    }
+
     iterator begin() { return &attrs[0]; }
     iterator end() { return &attrs[size_]; }