52 lines
1.3 KiB
Dart
52 lines
1.3 KiB
Dart
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part of symbol_table;
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/// Holds an immutable symbol, the value of which is set once and only once.
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@deprecated
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class Constant<T> extends Variable<T> {
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Constant(String name, T value) : super._(name, null, value: value) {
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lock();
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}
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}
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/// Holds a symbol, the value of which may change or be marked immutable.
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class Variable<T> {
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final String name;
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final SymbolTable<T>? symbolTable;
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Visibility visibility = Visibility.public;
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bool _locked = false;
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T? _value;
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Variable._(this.name, this.symbolTable, {T? value}) {
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_value = value;
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}
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/// If `true`, then the value of this variable cannot be overwritten.
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bool get isImmutable => _locked;
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/// This flag has no meaning within the context of this library, but if you
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/// are implementing some sort of interpreter, you may consider acting based on
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/// whether a variable is private.
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@deprecated
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bool get isPrivate => visibility == Visibility.private;
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T? get value => _value;
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void set value(T? value) {
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if (_locked)
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throw new StateError(
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'The value of constant "$name" cannot be overwritten.');
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_value = value;
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}
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/// Locks this symbol, and prevents its [value] from being overwritten.
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void lock() {
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_locked = true;
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}
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/// Marks this symbol as private.
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@deprecated
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void markAsPrivate() {
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visibility = Visibility.private;
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}
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}
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