From 9611db8130bb1dd1e8175ed6de46b0a1586998d7 Mon Sep 17 00:00:00 2001
From: Jose Luis Blanco Claraco <joseluisblancoc@gmail.com>
Date: Thu, 3 Dec 2020 09:06:44 +0100
Subject: [PATCH] SymbolGenerator: add chr() and made constexpr-capable

---
 gtsam/inference/Symbol.h          | 5 +++--
 gtsam/inference/tests/testKey.cpp | 6 ++++++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/gtsam/inference/Symbol.h b/gtsam/inference/Symbol.h
index 469082f16..42cdbb1c3 100644
--- a/gtsam/inference/Symbol.h
+++ b/gtsam/inference/Symbol.h
@@ -167,10 +167,11 @@ inline Key Z(std::uint64_t j) { return Symbol('z', j); }
 /** Generates symbol shorthands with alternative names different than the
  * one-letter predefined ones. */
 class SymbolGenerator {
-  const char c_;
+  const unsigned char c_;
 public:
-  SymbolGenerator(const char c) : c_(c) {}
+  constexpr SymbolGenerator(const unsigned char c) : c_(c) {}
   Symbol operator()(const std::uint64_t j) const { return Symbol(c_, j); }
+  constexpr unsigned char chr() const { return c_; }
 };
 
 /// traits
diff --git a/gtsam/inference/tests/testKey.cpp b/gtsam/inference/tests/testKey.cpp
index 64674c36f..98c5d36bf 100644
--- a/gtsam/inference/tests/testKey.cpp
+++ b/gtsam/inference/tests/testKey.cpp
@@ -59,6 +59,12 @@ TEST(Key, SymbolGenerator) {
   EXPECT(assert_equal(a1, ddz1));
 }
 
+/* ************************************************************************* */
+TEST(Key, SymbolGeneratorConstexpr) {
+  constexpr auto Z = gtsam::SymbolGenerator('x');
+  EXPECT(assert_equal(Z.chr(), 'x'));
+}
+
 /* ************************************************************************* */
 template<int KeySize>
 Key KeyTestValue();