Language Implementation Patterns

Pattern 20

Computing Static Expression Types

Purpose

This pattern explains how to statically compute the type of expressions in languages with explicit type declarations like C.

You’ll be able to extrapolate from this pattern everything you’d need to build a static type analyzer for C, C++, Java, or C#. Every compiler for those languages implements an extended version of this pattern. So do static bug analyzers such as FindBugs^[23] and Coverity.^[24]

Discussion

Type computation is an extremely broad topic. To make things more concrete, we’ll focus on the type computation rules for Cymbol itemized here:

Subexpression	Result Type
true, false	boolean.
Character literal	char.
Integer literal	int.
Floating-point literal	float.
id	The declared type of the variable ...