Platform Folding

The Platform Folding optimizer resolves React Native Platform.select calls and Platform.OS uses before the other Boost optimizers run. While Metro and Expo already perform similar release transforms in a later stage of the pipeline, that is too late for Boost to optimize any JSX and styles that make use of the Platform module. This early pass can therefore remove these runtime helpers earlier and increase optimization coverage of other Boost optimizers.

import { Platform } from 'react-native';

const color = Platform.select({ ios: 'blue', android: 'green', default: 'red' });
const cacheKey = `${Platform.OS}-cache`;
const screen = Platform.OS === 'ios' ? <IOSScreen /> : <AndroidScreen />;
if (Platform.OS === 'android') require('./install-android');

For an iOS build, this becomes the equivalent of:

const color = 'blue';
const cacheKey = 'ios-cache';
const screen = <IOSScreen />;

Platform.select follows React Native's fallback order: the target platform, native, then default. The optimizer requires a plain object literal. It skips computed keys, spreads, getters, and additional arguments. Branch folding requires a strict (=== or !==) comparison between Platform.OS and a string literal.

Configuration

The optimizer is enabled by default. You can disable it in metro.config.js:

module.exports = withBoostConfig(config, {
  optimizations: {
    'platform-folding': 'off',
  },
});