rdotm(R.m) is the Objective-C resource definition generator like Android app's R.java.

A tool to generate code that makes you possible to access color resources via method:
<color name="title">#FF0099CC</string> -> [R color_title]

Hex color expressions are converted when executing this tool.
(Generated colors are written using [UIColor colorWithRed:green:blue:alpha].)

So if you have a utility method like [UIColor colorWithHexString] to convert hex strings on runtime, your app could be a little bit faster.

A tool to generate code that makes you possible to access integer resources via method:
<integer name="max_length_name">20</string> -> [R integer_max_length_name]
<item name="max_length_name" type="integer">20</string> -> [R integer_max_length_name]

A tool to generate code that makes you possible to access string resources via method:
<string name="something">anything</string> -> [R string_something]

Because you can share resource files with Android app project.

You can use Localizable.strings and NSLocalizedString, but it has a problem that even if you have some typos you will not be noticed while compiling them.

For example, if you define a string like this:

"something" = "anything";

then you can refer this string with the following code:

// OK, this will be @"anything"
NSString *s = NSLocalizedString(@"something", nil);

but you may mistype it:

// This is typo, but it won't cause any compile errors
NSString *s = NSLocalizedString(@"s0mething", nil);

This means that you must run the app manually and detect this bug with your eyes, or write some test codes to detect it.

A tool to generate code that makes you possible to access image resources via method:
res/drawable/star@2x.png -> [R drawable_star]

Suffix like @2x will be ignored, so star.png and star@2x.png will be identified as the same images.

There are several methods to install rdotm.

Get the latest release binary is the easiest way to install it if you don't have golang environment.
Note that the latest release may be stable but not always the "latest".
If you want to use the truly latest version, install it with go get or gom.

For OS X users, you can install it with Homebrew.

$ brew tap ksoichiro/rdotm
$ brew install rdotm

If you want to install it as a global command, try this:

$ go get github.com/ksoichiro/rdotm

If you use this tool in a Xcode build process, using gom is the recommended way.
With this tool, you can manage rdotm's version in your VCS.

$ go get github.com/mattn/gom
$ echo "gom 'github.com/ksoichiro/rdotm'" > Gomfile
$ gom install
$ tree -L 5
.
├── Gomfile
└── _vendor
    ├── bin
    │   └── rdotm
    └── src
        └── github.com
            └── ksoichiro
                └── rdotm

Now you can use rdotm tool like following command:

$ PATH=_vendor/bin:$PATH rdotm -res ...
or
$ _vendor/bin/rdotm -res ...

See sample codes in testdata/xcode directories for details.

$ rdotm -res /path/to/res -out /path/to/output/dir

res directory should be the Android app's resource structure.
Example:

res
├── drawable
│   ├── star.png
│   └── star@2x.png
└── values
    ├── colors.xml
    └── strings.xml

res/values/strings.xml

<resources>
    <string name="title_top">Demo</string>
    <string name="label_message">Hello, world!</string>
</resources>

res/values/integers.xml

<resources>
    <integer name="sample_number">10</item>
</resources>

res/values/colors.xml

<resources>
    <color name="default_bg">#bef</color>
    <color name="default_text">#990099cc</color>
</resources>

res/values/arrays.xml

<resources>
    <integer-array name="foobar">
        <item>10</item>
        <item>20</item>
        <item>30</item>
    </integer-array>

    <string-array name="blurblur">
        <item>hoge</item>
        <item>fuga</item>
        <item>piyo</item>
    </string-array>
</resources>

res/drawables

res/drawable
├── star.png
└── star@2x.png

R.h

// DO NOT EDIT.
// This file is automatically generated by rdotm tool.
// https://github.com/ksoichiro/rdotm

#import <UIKit/UIKit.h>

@interface R : NSObject

/** Demo */
+ (NSString *)string_title_top;
/** Hello, world! */
+ (NSString *)string_label_message;
/** 10 */
+ (NSInteger)integer_sample_number;
/** #bef */
+ (UIColor *)color_default_bg;
/** #990099cc */
+ (UIColor *)color_default_text;
+ (UIImage *)drawable_star;
+ (NSArray *)array_integer_foobar;
+ (NSArray *)array_string_blurblur;

@end

R.m

// DO NOT EDIT.
// This file is automatically generated by rdotm tool.
// https://github.com/ksoichiro/rdotm

#import "R.h"

@implementation R

+ (NSString *)string_title_top { return @"Demo"; }
+ (NSString *)string_label_message { return @"Hello, world!"; }
+ (NSInteger)integer_sample_number { return 10; }
+ (UIColor *)color_default_bg { return [UIColor colorWithRed:187/255.0 green:238/255.0 blue:255/255.0 alpha:255/255.0]; }
+ (UIColor *)color_default_text { return [UIColor colorWithRed:0/255.0 green:153/255.0 blue:204/255.0 alpha:153/255.0]; }
+ (UIImage *)drawable_star { return [UIImage imageNamed:@"star"]; }
+ (NSArray *)array_integer_foobar { return @[@10, @20, @30]; }
+ (NSArray *)array_string_blurblur { return @[@"hoge", @"fuga", @"piyo"]; }

@end

R.m

// DO NOT EDIT.
// This file is automatically generated by rdotm tool.
// https://github.com/ksoichiro/rdotm

#import "R.h"

@implementation R

+ (NSString *)string_title_top { return NSLocalizedStringFromTable(@"title_top", @"R", nil); }
+ (NSString *)string_label_message { return NSLocalizedStringFromTable(@"label_message", @"R", nil); }
+ (NSInteger)integer_sample_number { return 10; }
+ (UIColor *)color_default_bg { return [UIColor colorWithRed:187/255.0 green:238/255.0 blue:255/255.0 alpha:255/255.0]; }
+ (UIColor *)color_default_text { return [UIColor colorWithRed:0/255.0 green:153/255.0 blue:204/255.0 alpha:153/255.0]; }
+ (UIImage *)drawable_star { return [UIImage imageNamed:@"star"]; }

@end

Base.lproj/R.strings

// DO NOT EDIT.
// This file is automatically generated by rdotm tool.
// https://github.com/ksoichiro/rdotm

"title_top" = "Demo";
"label_message" = "Hello, world!";

ja.lproj/R.strings

// DO NOT EDIT.
// This file is automatically generated by rdotm tool.
// https://github.com/ksoichiro/rdotm

"title_top" = "デモ";
"label_message" = "こんにちは、世界！";

Copyright (c) 2014 Soichiro Kashima
Licensed under MIT license.
See the bundled LICENSE file for details.