The Shape of Code

Operator overloading, like many programming language constructs, was first supported in the 1960s (Algol 68 also provided a means to specify a precedence for the operator). C++ is perhaps the most widely used language supporting operator overloading; but not redefining their precedence.

I have always thought that operator overloading was more talked about than actually used (despite its long history, I have not been able to find any published usage information). A previous post noted that the CodeQL databases hosted by GitHub provides the data needed to measure usage, and having wrestled with the documentation (ql scripts used), C++ operator overload usage data is available.

The table below shows the total uses of overloaded and ‘usual’ binary operators in the source code (excluding headers) of 77 C++ repositories on GitHub (the 100 repositories C/C+ MRVA). The table is ordered by total occurrences of overloads, with the Percentage column showing the percentage use of overloaded operators against the total for the respective operator (i.e., ; code and data):

Binary  Overload    Usual     Total   Percentage
  <<     103,855    20,463   124,318     83.5
  ==      21,845   118,037   139,882     15.6
  !=      14,749    69,273    84,022     17.6
   *      12,849    57,906    70,755     18.2
   +      10,928   103,072   114,000      9.6
  &&       8,183    64,148    72,331     11.3
   -       5,064    77,775    82,839      6.1
  <=       3,960    18,344    22,304     17.8
   &       3,320    27,388    30,708     10.8
   <       1,351    93,393    94,744      1.4
  >>       1,082    11,038    12,120      8.9
   /       1,062    29,023    30,085      3.5
   >        537     44,556    45,093      1.2
  >=        473     27,738    28,211      1.7
   |        293     13,959    14,252      2.0
   ^         71      1,248     1,319      5.4
  <=>        13         12        25     52.0
   %         11      9,338     9,349      0.1
  ||          9     53,829    53,838      0.017

Use of the overloaded << operator is driven by standard library I/O, rather than left shifting.

There are seven operators where 10-20% of the usage is overloaded, which is a lot higher than I was expecting (not that I am a C++ expert).

How much does overloaded binary operator usage vary across projects? In the plot below, each vertical colored violin plot shows the distribution of overload usage for one operator across all 77 projects (the central black lines denote the range of the central 50% of the points; code and data):

While there is some variation between these 77 projects, in most cases a non-trivial percentage of an operator's usage is overloaded.