How can I provide template specializations for typedefs of the same type?

Question

A 3rd party SDK defines several typedefs, e.g.:

typedef unsigned char SDK_BYTE
typedef double SDK_DOUBLE
typedef unsigned char SDK_BOOLEAN

Answer 1

You could do it like this:

SDK_BYTE asByte(SdkVariant & var)
{
  SDK_BYTE byte;
  bool const ok = var.toByte(byte);
  if (!ok) diePainfully();
  return byte;
}

SDK_DOUBLE asDouble(SdkVariant & var)
{
  SDK_DOUBLE d;
  bool const ok = var.toDouble(d);
  if (!ok) diePainfully();
  return d;
}

SDK_BOOLEAN asBoolean(SdkVariant & var)
{
  SDK_BOOLEAN b;
  bool const ok = var.toBool(b);
  if (!ok) diePainfully();
  return b;
}

static const bool byteAndBooleanAreTheSame = std::is_same::value;

template 
struct VariantCastImpl
{
  template  T cast(SdkVariant & var) const;

  template <> SDK_DOUBLE cast(SdkVariant & var) const { return asDouble(var); }
  template <> SDK_BYTE cast(SdkVariant & var) const { return asByte(var); }
  template <> SDK_BOOLEAN cast(SdkVariant & var) const { return asBoolean(var); }
};

template <>
struct VariantCastImpl
{
  template  T cast(SdkVariant & var) const;

  template <> SDK_DOUBLE cast(SdkVariant & var) const { return asDouble(var); }
  template <> SDK_BYTE cast(SdkVariant & var) const
  {
    if (var.type() == SdkVariant::SdkByte)
    {
      return asByte(var);
    }
    else if (var.type() == SdkVariant::SdkBoolean)
    {
      return asBoolean(var);
    }
    else
    {
      diePainfully();
      return SDK_BYTE(); // dummy return, I assume diePainfully throws something
    }
  }
};

template 
T variant_cast(SdkVariant & var)
{
  return VariantCastImpl().cast(var);
};