localize method Null safety

ThemeData localize(
  1. ThemeData baseTheme,
  2. TextTheme localTextGeometry

Returns a new theme built by merging the text geometry provided by the localTextGeometry theme with the baseTheme.

For those text styles in the baseTheme whose TextStyle.inherit is set to true, the returned theme's text styles inherit the geometric properties of localTextGeometry. The resulting text styles' TextStyle.inherit is set to those provided by localTextGeometry.


static ThemeData localize(ThemeData baseTheme, TextTheme localTextGeometry) {
  // WARNING: this method memoizes the result in a cache based on the
  // previously seen baseTheme and localTextGeometry. Memoization is safe
  // because all inputs and outputs of this function are deeply immutable, and
  // the computations are referentially transparent. It only short-circuits
  // the computation if the new inputs are identical() to the previous ones.
  // It does not use the == operator, which performs a costly deep comparison.
  // When changing this method, make sure the memoization logic is correct.
  // Remember:
  // There are only two hard things in Computer Science: cache invalidation
  // and naming things. -- Phil Karlton
  assert(baseTheme != null);
  assert(localTextGeometry != null);

  return _localizedThemeDataCache.putIfAbsent(
    _IdentityThemeDataCacheKey(baseTheme, localTextGeometry),
    () {
      return baseTheme.copyWith(
        primaryTextTheme: localTextGeometry.merge(baseTheme.primaryTextTheme),
        accentTextTheme: localTextGeometry.merge(baseTheme.accentTextTheme),
        textTheme: localTextGeometry.merge(baseTheme.textTheme),