add support for Func() and BoolFunc() #426

Add support for two features which landed in the 'flag' package
from the standard library: Func() and BoolFunc()
and their two pflag specific versions: FuncP() and BoolFuncP()

fixes #426

1 files changed, 37 insertions, 0 deletions

diff --git a/func.go b/func.go
new file mode 100644
index 0000000..e5f5436
--- /dev/null
+++ b/func.go
@@ -0,0 +1,37 @@
+package pflag
+
+// -- func Value
+type funcValue func(string) error
+
+func (f funcValue) Set(s string) error { return f(s) }
+
+func (f funcValue) Type() string { return "func" }
+
+func (f funcValue) String() string { return "" } // same behavior as stdlib 'flag' package
+
+// Func defines a func flag with specified name, callback function and usage string.
+//
+// The callback function will be called every time "--{name}={value}" (or equivalent) is
+// parsed on the command line, with "{value}" as an argument.
+func (f *FlagSet) Func(name string, usage string, fn func(string) error) {
+	f.FuncP(name, "", usage, fn)
+}
+
+// FuncP is like Func, but accepts a shorthand letter that can be used after a single dash.
+func (f *FlagSet) FuncP(name string, shorthand string, usage string, fn func(string) error) {
+	var val Value = funcValue(fn)
+	f.VarP(val, name, shorthand, usage)
+}
+
+// Func defines a func flag with specified name, callback function and usage string.
+//
+// The callback function will be called every time "--{name}={value}" (or equivalent) is
+// parsed on the command line, with "{value}" as an argument.
+func Func(name string, fn func(string) error, usage string) {
+	CommandLine.FuncP(name, "", usage, fn)
+}
+
+// FuncP is like Func, but accepts a shorthand letter that can be used after a single dash.
+func FuncP(name, shorthand string, fn func(string) error, usage string) {
+	CommandLine.FuncP(name, shorthand, usage, fn)
+}