Added option examples

examples/07_OptionArgs.rs

@@ -0,0 +1,71 @@
+extern crate clap;
+
+use clap::{App, Arg};
+
+fn main() {
+
+	// Option arguments are those that take an additional value, such as "-c value". In clap they
+	// support three types of specification, those with short() as "-o some", or those with long()
+	// as "--option value" or "--option=value"
+	//
+	// Options also support a multiple setting, which is dicussed in the example below.
+    let matches = App::new("MyApp")
+    					// Regular App configuration goes here...
+
+    					// Assume we an application that accepts an input file via the "-i file"
+    					// or the "--input file" (as wel as "--input=file"). 
+    					// Below every setting supported by option arguments is discussed.
+    					// NOTE: You DO NOT need to specify each setting, only those which apply
+    					// to your particular case.
+                        .arg(Arg::new("input")
+                                    .help("the input file to use") // Displayed when showing help info
+                                    .takes_value(true)			   // MUST be set to true in order to be an "option" argument
+                                    .short("i")					   // This argument is triggered with "-i"
+                                    .long("input")				   // This argument is triggered with "--input"
+                                    .multiple(true)				   // Set to true if you wish to allow multiple occurrences
+                                    							   // such as "-i file -i other_file -i third_file"
+                                    .required(true)				   // By default this argument MUST be present
+                                    							   // NOTE: mutual exclusions take precedence over
+                                    							   // required arguments
+                                    .requires("config")			   // Says, "If the user uses "input", they MUST
+                                    							   // also use this other 'config' arg too"
+                                    							   // Can also specifiy a list using 
+                                    							   // requires_all(Vec<&str>)
+                                    .mutually_excludes("output")   // Opposite of requires(), says "if the
+                                    							   // user uses -a, they CANNOT use 'output'"
+                                    							   // also has a mutually_excludes_all(Vec<&str>)
+                        )
+						// NOTE: In order to compile this example, comment out mutually_excludes()
+						// and requires() because we have not defined an "output" or "config"
+						// argument.
+                        .get_matches();
+
+    // We can find out whether or not "input" was used 
+    if matches.is_present("input") {
+    	println!("An input file was specified");
+    }
+    
+    // We can also get the value for "input"
+    //
+    // NOTE: If we specified multiple(), this will only return the _FIRST_
+    // occurrence
+    if let Some(ref in_file) = matches.value_of("input") {
+    	println!("An input file: {}", in_file);
+    }
+
+    // If we specified the multiple() setting we can get all the values
+    if let Some(ref in_v) = matches.values_of("input") {
+    	for in_file in in_v.iter() {
+    		println!("An input file: {}", in_file);
+    	}
+    }
+
+    // We can see how many times the option was used with the occurrences_of() method
+    //
+    // NOTE: Just like with flags, if we did not specify the multiple() setting this will only
+    // return 1 no matter how many times the argument was used (unless it wasn't used at all, in
+    // in which case 0 is returned)
+    println!("The \"input\" argument was used {} times", matches.occurrences_of("input"));
+
+    // Continued program logic goes here...
+}