Abseil Stringify

By Phoebe Liang, Abseil Engineer

We are pleased to introduce an easier way to format user-defined types as strings in Abseil: AbslStringify(). This API allows user-defined types to be printed more easily using absl::StrFormat() and absl::StrCat().

To “stringify” a custom type, define a friend function template named AbslStringify():

struct Point 
  template <typename Sink>
  friend void AbslStringify(Sink& sink, const Point& p) {
    absl::Format(&sink, "(%d, %d)", p.x, p.y);
  }

  int x;
  int y;
}

absl::StrCat() will work right out of the box like so:

absl::StrCat("The point is ", p);

To print custom types with absl::StrFormat(), use the new type specifier %v:

absl::StrFormat("The point is %v", p);

%v uses type deduction to print an argument and supports any user-defined type that provides an AbslStringify() definition. Most types that are supported natively by absl::StrFormat() are also supported by %v. For a full list of supported types, see the StrFormat Guide.