"42" + 1

What, if anything, should a mixed-type expression like "42" + 1 mean?

The sanest result is a compile-time error, as in Rust.

	$ cargo check
	Checking rust v0.1.0 (/Users/jeff/var/play/rust)
	error[E0369]: cannot add `{integer}` to `&str`
	--> src/main.rs:2:25
	|
	2 | println!("{}", "42" + 1);
	| ---- ^ - {integer}
	| |
	| &str

view raw nested-42-1-rust.sh hosted with ❤ by GitHub

Slightly less sane is a compiler that correctly diagnoses the issue, but nevertheless produces a binary that does something wacky at run-time.

	$ cc main.c
	main.c:4:13: warning: adding 'int' to a string does not append to the string [-Wstring-plus-int]
	puts("42" + 1);
	~~~~~^~~
	$ ./a.out
	2

view raw nested-42-1-c.sh hosted with ❤ by GitHub

The next least insane result is a run-time error, as in Python.

	$ python3 -c 'print("42" + 1)'
	Traceback (most recent call last):
	File "<string>", line 1, in <module>
	TypeError: can only concatenate str (not "int") to str

view raw nested-42-1-python.sh hosted with ❤ by GitHub

The most guano crazy thing you could possibly do is to silently and implicitly convert one side of the expression to the other's type, as in Perl or JavaScript.

	$ perl -le 'print "42" + 1'
	43
	$ node -p '"42" + 1'
	421

view raw nested-42-1-perl.sh hosted with ❤ by GitHub

Guess what Java does?

	public class Main {
	public static void main(String[] args) {
	System.out.println("42" + 1);
	}
	}

view raw nested-42-1-Main.java hosted with ❤ by GitHub

	$ javac Main.java && java Main
	421

view raw nested-42-1-java.sh hosted with ❤ by GitHub

Java gives the initial impression of being a strongly typed language, but it has an awful lot of gotchas. In fact, Java is basically a dark room full of razor blades, but we can blunt those blades else-post. For now, simply consider: If you were writing the next big programming language, how would it handle "42" + 1?