build method

Implementation

ChildSemanticsConfigurationsResult build() {
  assert((){
    final Set<SemanticsConfiguration> seenConfigs = <SemanticsConfiguration>{};
    for (final SemanticsConfiguration config in <SemanticsConfiguration>[..._mergeUp, ..._siblingMergeGroups.flattened]) {
      assert(
        seenConfigs.add(config),
        'Duplicated SemanticsConfigurations. This can happen if the same '
        'SemanticsConfiguration was marked twice in markAsMergeUp and/or '
        'markAsSiblingMergeGroup'
      );
    }
    return true;
  }());
  return ChildSemanticsConfigurationsResult._(_mergeUp, _siblingMergeGroups);
}