types - What is the right way to convert Variant to proper type?

Question

I use mysql-native that return Variant data type. I need to convert it to standard types like int, string etc.

D have std.conv, but std.variant also have methods for concretion.

I can't understand what difference between: get, coerce, toString and to (from std.conv).

Also it's sound very strange that convertsTo is return bool. By it's name I expected that it should do convention. IMHO isConvertable is more proper name for it.

Answer 1

有三种方法可以从Variant类型中获取值：

• Variant.peek!T：如果对象当前持有的值Variant是 类型T，则返回指向该值的指针。如果它持有不同类型的值，则返回 null。

  Variant v = "42";
  string* ptr = v.peek!string;
  assert(ptr !is null && *ptr == "42");
  

• Variant.get!T: 如果对象当前持有的值Variant是 类型T，则返回它的值。否则，VariantException抛出 a。

  Variant v = "42";
  assertThrown!VariantException(v.get!int);
  assertNotThrown!VariantException(v.get!string);
  

• Variant.coerce!T：返回对象当前持有的值Variant，显式转换为 type T。如果该值无法转换为 type T，则Exception抛出 an 。

  Variant v = "42";
  string s = v.coerce!string;
  assert(s == "42");
  int i = v.coerce!int;
  assert(i == 42);