[libcamera-devel] [RFC PATCH v2 1/9] libcamera: Value: Provide abstract value class

[Kieran Bingham]

To facilitate passing typed data generically, implement a class which stores
the type and value as efficiently as possible.

Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
---
 include/libcamera/meson.build |   1 +
 include/libcamera/value.h     |  63 ++++++++++
 src/libcamera/meson.build     |   1 +
 src/libcamera/value.cpp       | 226 ++++++++++++++++++++++++++++++++++
 4 files changed, 291 insertions(+)
 create mode 100644 include/libcamera/value.h
 create mode 100644 src/libcamera/value.cpp

diff --git a/include/libcamera/meson.build b/include/libcamera/meson.build
index 201832105457..eb2211ae1fc3 100644
--- a/include/libcamera/meson.build
+++ b/include/libcamera/meson.build
@@ -12,6 +12,7 @@ libcamera_api = files([
     'signal.h',
     'stream.h',
     'timer.h',
+    'value.h',
     'version.h',
 ])
 
diff --git a/include/libcamera/value.h b/include/libcamera/value.h
new file mode 100644
index 000000000000..00c5d53d5cc0
--- /dev/null
+++ b/include/libcamera/value.h
@@ -0,0 +1,63 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * value.h - Abstract value handling
+ */
+
+#include <map>
+
+#ifndef __LIBCAMERA_VALUE_H__
+#define __LIBCAMERA_VALUE_H__
+
+namespace libcamera {
+
+enum ValueType : uint8_t {
+	ValueNull,
+	ValueBool,
+	ValueInteger,
+	ValueInteger64,
+	ValueString,
+};
+
+class Value
+{
+public:
+	Value();
+	Value(bool value);
+	Value(int value);
+	Value(const char *value);
+	Value(const std::string &value);
+
+	ValueType type() const { return type_; };
+	bool isNull() const { return type_ == ValueNull; };
+
+	void set(bool value);
+	void set(int value);
+	void set(int64_t value);
+	void set(const char *value);
+	void set(const std::string &value);
+
+	bool getBool() const;
+	int getInt() const;
+	int getInt64() const;
+	std::string getString() const;
+
+	std::string toString() const;
+
+private:
+	ValueType type_;
+
+	union {
+		bool bool_;
+		int integer_;
+		int64_t integer64_;
+	};
+	std::string string_;
+};
+
+std::ostream &operator<<(std::ostream &stream, const Value &value);
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_VALUE_H__ */
diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
index 68c7ce14b5b4..8e68373118df 100644
--- a/src/libcamera/meson.build
+++ b/src/libcamera/meson.build
@@ -27,6 +27,7 @@ libcamera_sources = files([
     'v4l2_device.cpp',
     'v4l2_subdevice.cpp',
     'v4l2_videodevice.cpp',
+    'value.cpp',
     'version.cpp',
 ])
 
diff --git a/src/libcamera/value.cpp b/src/libcamera/value.cpp
new file mode 100644
index 000000000000..f713907b38dd
--- /dev/null
+++ b/src/libcamera/value.cpp
@@ -0,0 +1,226 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * value.cpp - Abstract value handling
+ */
+
+#include <limits.h>
+#include <sstream>
+#include <string>
+
+#include <libcamera/value.h>
+
+#include "log.h" // For ASSERT()
+
+/**
+ * \file value.h
+ * \brief Handles variant value types as an abstract object
+ */
+
+namespace libcamera {
+
+/**
+ * \enum ValueType
+ * Determines the type of value represented by a \a Value
+ * \var ValueNull
+ * Identifies an unset value
+ * \var ValueBool
+ * Identifies controls storing a boolean value
+ * \var ValueInteger
+ * Identifies controls storing an integer value
+ * \var ValueString
+ * Identifies controls storing a string value
+ */
+
+/**
+ * \class Value
+ * \brief Abstract a value for a common data exchange
+ */
+
+/**
+ * \brief Construct an empty Value.
+ * The Value must be \a set() before being used.
+ */
+Value::Value()
+	: type_(ValueNull)
+{
+}
+
+/**
+ * \brief Construct a Boolean Value
+ * \param[in] value Boolean value to store
+ */
+Value::Value(bool value)
+	: type_(ValueBool), bool_(value)
+{
+}
+
+/**
+ * \brief Construct an integer Value
+ * \param[in] value Integer value to store
+ */
+Value::Value(int value)
+	: type_(ValueInteger), integer_(value)
+{
+}
+
+/**
+ * \brief Construct a string Value
+ * \param[in] value String representation to store
+ */
+Value::Value(const char *value)
+	: type_(ValueString), string_(value)
+{
+}
+
+/**
+ * \brief Construct a string Value
+ * \param[in] value String representation to store
+ */
+Value::Value(const std::string &value)
+	: type_(ValueString), string_(value)
+{
+}
+
+/**
+ * \fn Value::type
+ * \brief Return the type of value represented by the object
+ */
+
+/**
+ * \fn Value::isNull
+ * \brief Determines if the Value is initialised
+ * \return true if the value type is ValueNull, false otherwise
+ */
+
+/**
+ * \brief Set the value with a boolean
+ * \param[in] value Boolean value to store
+ */
+void Value::set(bool value)
+{
+	type_ = ValueBool;
+	bool_ = value;
+}
+
+/**
+ * \brief Set the value with an integer
+ * \param[in] value Integer value to store
+ */
+void Value::set(int value)
+{
+	type_ = ValueInteger;
+	integer_ = value;
+}
+
+/**
+ * \brief Set the value with a 64 bit integer
+ * \param[in] value Integer value to store
+ */
+void Value::set(int64_t value)
+{
+	type_ = ValueInteger64;
+	integer64_ = value;
+}
+
+/**
+ * \brief Set the value with a string representation
+ * \param[in] value String value to store
+ */
+void Value::set(const char *value)
+{
+	type_ = ValueString;
+	string_ = value;
+}
+
+/**
+ * \brief Set the value with a string representation
+ * \param[in] value String value to store
+ */
+void Value::set(const std::string &value)
+{
+	type_ = ValueString;
+	string_ = value;
+}
+
+/**
+ * \brief Get the boolean value.
+ *
+ * The Value type must be Boolean.
+ */
+bool Value::getBool() const
+{
+	ASSERT(type_ == ValueBool);
+
+	return bool_;
+}
+
+/**
+ * \brief Get the integer value.
+ *
+ * The Value type must be Integer.
+ */
+int Value::getInt() const
+{
+	ASSERT(type_ == ValueInteger);
+
+	return integer_;
+}
+
+/**
+ * \brief Get the 64bit integer value.
+ *
+ * The Value type must be Integer64.
+ */
+int Value::getInt64() const
+{
+	ASSERT(type_ == ValueInteger64);
+
+	return integer64_;
+}
+
+/**
+ * \brief Get the string value.
+ *
+ * The Value type must be String.
+ */
+std::string Value::getString() const
+{
+	ASSERT(type_ == ValueString);
+
+	return string_;
+}
+
+/**
+ * \brief Prepare a string representation of the Value
+ */
+std::string Value::toString() const
+{
+	switch (type_) {
+	case ValueNull:
+		return "<NULL>";
+	case ValueBool:
+		return bool_ ? "True" : "False";
+	case ValueInteger:
+		return std::to_string(integer_);
+	case ValueInteger64:
+		return std::to_string(integer64_);
+	case ValueString:
+		return string_;
+	}
+
+	/* Unreachable */
+	return "<ValueType Error>";
+}
+
+/**
+ * \brief Provide a string stream representation of the Value \a value to
+ * the \a stream.
+ */
+std::ostream &operator<<(std::ostream &stream, const Value &value)
+{
+	return stream << value.toString();
+}
+
+} /* namespace libcamera */
-- 
2.20.1