89 lines
2.6 KiB
Dart
89 lines
2.6 KiB
Dart
// Copyright (c) 2015 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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part of cassowary;
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class Expression extends EquationMember {
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final List<Term> terms;
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final double constant;
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double get value => terms.fold(constant, (value, term) => value + term.value);
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Expression(this.terms, this.constant);
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Constraint _createConstraint(double value, Relation relation) {
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return new Constraint(
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new Expression(this.terms, this.constant + value), relation);
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}
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Constraint operator >=(double value) =>
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_createConstraint(-value, Relation.greaterThanOrEqualTo);
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Constraint operator <=(double value) =>
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_createConstraint(-value, Relation.lessThanOrEqualTo);
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operator ==(double value) => _createConstraint(-value, Relation.equalTo);
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Expression operator +(EquationMember m) {
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if (m is ConstantMember) {
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return new Expression(new List.from(this.terms), this.constant + m.value);
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}
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if (m is Variable) {
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return new Expression(
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new List.from(this.terms)..add(new Term(m, 1.0)), this.constant);
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}
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if (m is Term) {
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return new Expression(new List.from(this.terms)..add(m), this.constant);
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}
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if (m is Expression) {
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return new Expression(new List.from(this.terms)..addAll(m.terms),
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this.constant + m.constant);
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}
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assert(false);
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return null;
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}
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Expression operator -(EquationMember m) {
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if (m is ConstantMember) {
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return new Expression(new List.from(this.terms), this.constant - m.value);
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}
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if (m is Variable) {
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return new Expression(
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new List.from(this.terms)..add(new Term(m, -1.0)), this.constant);
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}
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if (m is Term) {
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return new Expression(new List.from(this.terms)
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..add(new Term(m.variable, -m.coefficient)), this.constant);
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}
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if (m is Expression) {
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var copiedTerms = new List<Term>.from(this.terms);
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m.terms.forEach(
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(t) => copiedTerms.add(new Term(t.variable, -t.coefficient)));
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return new Expression(copiedTerms, this.constant - m.constant);
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}
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assert(false);
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return null;
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}
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EquationMember operator *(double m) {
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var terms = this.terms.fold(new List<Term>(), (list, term) => list
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..add(new Term(term.variable, term.coefficient * m)));
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return new Expression(terms, this.constant);
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}
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// TODO(csg): Figure out how to dry this up.
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EquationMember operator /(double m) {
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var terms = this.terms.fold(new List<Term>(), (list, term) => list
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..add(new Term(term.variable, term.coefficient / m)));
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return new Expression(terms, this.constant);
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}
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}
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