From 27b2079f26ada24fe4dc656c26f9f7a800b850fb Mon Sep 17 00:00:00 2001
From: Mikael Lund <mlund@mac.com>
Date: Mon, 1 Jul 2024 17:34:55 +0200
Subject: [PATCH] Add get_optional json function

---
 src/core.h | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/core.h b/src/core.h
index da63ba660..0b96a0053 100644
--- a/src/core.h
+++ b/src/core.h
@@ -254,4 +254,17 @@ class Electrolyte
 void to_json(json& j, const Electrolyte& electrolyte);
 std::optional<Electrolyte> makeElectrolyte(const json& j); //!< Create ionic salt object from json
 
+/// Extract JSON value associated with `key` into `std::optional`
+///
+/// If the value does not exist, return `std::nullopt`
+///
+/// @throws If value exists but cannot be extracted as `T`.
+template<typename T> 
+std::optional<T> get_optional(const json &j, std::string_view key) {
+    if (const auto it = j.find(key); it != j.end()) {
+        return it->get<T>(); // may throw exception
+    }
+    return std::nullopt;
+}
+
 } // namespace Faunus