stdlib: add StringSwitch to LLVMSupport fork

stdlib/include/llvm/ADT/StringSwitch.h

@@ -0,0 +1,198 @@
+//===--- StringSwitch.h - Switch-on-literal-string Construct --------------===/
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//===----------------------------------------------------------------------===/
+//
+//  This file implements the StringSwitch template, which mimics a switch()
+//  statement whose cases are string literals.
+//
+//===----------------------------------------------------------------------===/
+#ifndef LLVM_ADT_STRINGSWITCH_H
+#define LLVM_ADT_STRINGSWITCH_H
+
+#include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Compiler.h"
+#include <cassert>
+#include <cstring>
+
+inline namespace __swift { inline namespace __runtime {
+namespace llvm {
+
+/// A switch()-like statement whose cases are string literals.
+///
+/// The StringSwitch class is a simple form of a switch() statement that
+/// determines whether the given string matches one of the given string
+/// literals. The template type parameter \p T is the type of the value that
+/// will be returned from the string-switch expression. For example,
+/// the following code switches on the name of a color in \c argv[i]:
+///
+/// \code
+/// Color color = StringSwitch<Color>(argv[i])
+///   .Case("red", Red)
+///   .Case("orange", Orange)
+///   .Case("yellow", Yellow)
+///   .Case("green", Green)
+///   .Case("blue", Blue)
+///   .Case("indigo", Indigo)
+///   .Cases("violet", "purple", Violet)
+///   .Default(UnknownColor);
+/// \endcode
+template<typename T, typename R = T>
+class StringSwitch {
+  /// The string we are matching.
+  const StringRef Str;
+
+  /// The pointer to the result of this switch statement, once known,
+  /// null before that.
+  Optional<T> Result;
+
+public:
+  explicit StringSwitch(StringRef S)
+  : Str(S), Result() { }
+
+  // StringSwitch is not copyable.
+  StringSwitch(const StringSwitch &) = delete;
+
+  // StringSwitch is not assignable due to 'Str' being 'const'.
+  void operator=(const StringSwitch &) = delete;
+  void operator=(StringSwitch &&other) = delete;
+
+  StringSwitch(StringSwitch &&other)
+    : Str(other.Str), Result(std::move(other.Result)) { }
+
+  ~StringSwitch() = default;
+
+  // Case-sensitive case matchers
+  StringSwitch &Case(StringLiteral S, T Value) {
+    if (!Result && Str == S) {
+      Result = std::move(Value);
+    }
+    return *this;
+  }
+
+  StringSwitch& EndsWith(StringLiteral S, T Value) {
+    if (!Result && Str.endswith(S)) {
+      Result = std::move(Value);
+    }
+    return *this;
+  }
+
+  StringSwitch& StartsWith(StringLiteral S, T Value) {
+    if (!Result && Str.startswith(S)) {
+      Result = std::move(Value);
+    }
+    return *this;
+  }
+
+  StringSwitch &Cases(StringLiteral S0, StringLiteral S1, T Value) {
+    return Case(S0, Value).Case(S1, Value);
+  }
+
+  StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
+                      T Value) {
+    return Case(S0, Value).Cases(S1, S2, Value);
+  }
+
+  StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
+                      StringLiteral S3, T Value) {
+    return Case(S0, Value).Cases(S1, S2, S3, Value);
+  }
+
+  StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
+                      StringLiteral S3, StringLiteral S4, T Value) {
+    return Case(S0, Value).Cases(S1, S2, S3, S4, Value);
+  }
+
+  StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
+                      StringLiteral S3, StringLiteral S4, StringLiteral S5,
+                      T Value) {
+    return Case(S0, Value).Cases(S1, S2, S3, S4, S5, Value);
+  }
+
+  StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
+                      StringLiteral S3, StringLiteral S4, StringLiteral S5,
+                      StringLiteral S6, T Value) {
+    return Case(S0, Value).Cases(S1, S2, S3, S4, S5, S6, Value);
+  }
+
+  StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
+                      StringLiteral S3, StringLiteral S4, StringLiteral S5,
+                      StringLiteral S6, StringLiteral S7, T Value) {
+    return Case(S0, Value).Cases(S1, S2, S3, S4, S5, S6, S7, Value);
+  }
+
+  StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
+                      StringLiteral S3, StringLiteral S4, StringLiteral S5,
+                      StringLiteral S6, StringLiteral S7, StringLiteral S8,
+                      T Value) {
+    return Case(S0, Value).Cases(S1, S2, S3, S4, S5, S6, S7, S8, Value);
+  }
+
+  StringSwitch &Cases(StringLiteral S0, StringLiteral S1, StringLiteral S2,
+                      StringLiteral S3, StringLiteral S4, StringLiteral S5,
+                      StringLiteral S6, StringLiteral S7, StringLiteral S8,
+                      StringLiteral S9, T Value) {
+    return Case(S0, Value).Cases(S1, S2, S3, S4, S5, S6, S7, S8, S9, Value);
+  }
+
+  // Case-insensitive case matchers.
+  StringSwitch &CaseLower(StringLiteral S, T Value) {
+    if (!Result && Str.equals_lower(S))
+      Result = std::move(Value);
+
+    return *this;
+  }
+
+  StringSwitch &EndsWithLower(StringLiteral S, T Value) {
+    if (!Result && Str.endswith_lower(S))
+      Result = Value;
+
+    return *this;
+  }
+
+  StringSwitch &StartsWithLower(StringLiteral S, T Value) {
+    if (!Result && Str.startswith_lower(S))
+      Result = std::move(Value);
+
+    return *this;
+  }
+
+  StringSwitch &CasesLower(StringLiteral S0, StringLiteral S1, T Value) {
+    return CaseLower(S0, Value).CaseLower(S1, Value);
+  }
+
+  StringSwitch &CasesLower(StringLiteral S0, StringLiteral S1, StringLiteral S2,
+                           T Value) {
+    return CaseLower(S0, Value).CasesLower(S1, S2, Value);
+  }
+
+  StringSwitch &CasesLower(StringLiteral S0, StringLiteral S1, StringLiteral S2,
+                           StringLiteral S3, T Value) {
+    return CaseLower(S0, Value).CasesLower(S1, S2, S3, Value);
+  }
+
+  StringSwitch &CasesLower(StringLiteral S0, StringLiteral S1, StringLiteral S2,
+                           StringLiteral S3, StringLiteral S4, T Value) {
+    return CaseLower(S0, Value).CasesLower(S1, S2, S3, S4, Value);
+  }
+
+  LLVM_NODISCARD
+  R Default(T Value) {
+    if (Result)
+      return std::move(*Result);
+    return Value;
+  }
+
+  LLVM_NODISCARD
+  operator R() {
+    assert(Result && "Fell off the end of a string-switch");
+    return std::move(*Result);
+  }
+};
+
+} // end namespace llvm
+}}
+
+#endif // LLVM_ADT_STRINGSWITCH_H