Tilde and caret version constraints in Composer

Recently, Composer changed their default version constraint from using ~ (tilde) to ^ (caret). Luckily for you, my friend Hannes Van De Vreken wrote a great article about the difference between the two:

There are also some syntactic sugar operators like ~ (tilde) and ^ (caret).

• ~4.1.3 means >=4.1.3,<4.2.0,
• ~4.1 means >=4.1.0,<5.0.0 (most used),
• ~0.4 means >=0.4.0,<1.0.0,
• ~4 means >=4.0.0,<5.0.0.

The caret sign is slightly different:

• ^4.1.3 (most used) means >=4.1.3,<5.0.0,
• ^4.1 means >=4.1.0,<5.0.0, same as ~4.1 but:
• ^0.4 means >=0.4.0,<0.5.0, this is different from ~0.4 and is more useful for defining backwards compatible version ranges.
• ^4 means >=4.0.0,<5.0.0 which is the same as ~4 and 4.*.

http://blog.madewithlove.be/post/tilde-and-caret-constraints/