panini::FeatureFlag Class Reference

Command for feature flags. More...

#include <FeatureFlag.hpp>

Inheritance diagram for panini::FeatureFlag:

Public Types
using	TCallback = std::function< void(Writer &writer)>

Public Member Functions
	FeatureFlag (bool condition, const std::string &context, TCallback &&callbackThen) noexcept
	FeatureFlag (bool condition, const std::string &context, TCallback &&callbackThen, TCallback &&callbackElse) noexcept
void	Visit (Writer &writer) override
Public Member Functions inherited from panini::Command
virtual	~Command ()=default

Detailed Description

Command for feature flags.

When the condition is true, the "then" callback is used to output code to the active writer. Otherwise, if the "else" callback is specified, this callback is used instead.

If the condition was true, the output is wrapped in single-line comments to make the generated code stand out more. These comments are omitted if the context parameter is left blank.

Feature flags are useful when you are working on generated code that depends on the context. For example, you have developed a new way to access the main database, but want to roll out this change in controlled stages instead of simultaneously.

Example:

std::string query = R"(INSERT INTO Users (name) VALUES ('Little Bobby Tables'))";
writer << FeatureFlag(
    newDbAccess,
    "new-db-access",
    [&query](Writer& writer) {
        writer << "db->WriteQueryFast(\"" << query << ";\");" << NextLine();
    },
    [&query](Writer& writer) {
        writer << "db->WriteQuery(\"" << query << ";\");" << NextLine();
    }
);

Output when the condition is true:

// new-db-access
db->WriteQueryFast("INSERT INTO Users (name) VALUES ('Little Bobby Tables');");
// new-db-access

Output when the condition is false:

db->WriteQuery("INSERT INTO Users (name) VALUES ('Little Bobby Tables');");

Member Typedef Documentation

TCallback

using panini::FeatureFlag::TCallback = std::function<void(Writer& writer)>

Callback type used for conditions.

Parameters

writer

Active writer.

Constructor & Destructor Documentation

FeatureFlag() [1/2]

panini::FeatureFlag::FeatureFlag ( bool  condition, const std::string &  context, TCallback &&  callbackThen  )

inlineexplicitnoexcept

Construct a FeatureFlag with a callback invoked when the condition is true.

Parameters

condition	Decide which callback to invoke
context	String added to comments for context
callbackThen	Invoked when condition is true

FeatureFlag() [2/2]

panini::FeatureFlag::FeatureFlag ( bool  condition, const std::string &  context, TCallback &&  callbackThen, TCallback &&  callbackElse  )

inlineexplicitnoexcept

Construct a FeatureFlag with a callback invoked when the condition is true and one when the condition is false.

Parameters

condition	Decide which callback to invoke
context	String added to comments for context
callbackThen	Invoked when condition is true
callbackElse	Invoked when condition is false

Member Function Documentation

Visit()

void panini::FeatureFlag::Visit ( Writer &  writer )

inlineoverridevirtual

Accepts a Writer to write chunks to the output.

Implements panini::Command.

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The documentation for this class was generated from the following file:

• include/commands/FeatureFlag.hpp