Analyser
e2immu is a static code analyser for Java.
Next to promoting the use of practical immutability, the e2immu project provides a static code analyser to help enforce the proper use of these immutability concepts.
The analyser is opinionated: it warns against a number of bad practices, such as:
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Assigning to a field outside the type of that field, is not allowed. Why? We believe that modification belongs to the type itself, as per the concept of a container. This may be too strong for certain situations. However, we insist that assignments to fields cannot be made outside the field itself.
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Non-private fields must be effectively final. Why? We make no distinction between the different forms of non-private-ness. This restriction is closely related to the previous one, but not quite the same.
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Methods which do not refer to the instance, must be marked
static. This is a trivial one, just make sure your IDE does it for you. -
Parameters should not be assigned to.
The analyser assumes that exceptions are used to detect illegal situations in the code: they should never be part of the normal program flow. It makes no distinction between static fields and instance fields for most concepts; the assumption being that non-immutable static fields are rarely used.
The analyser does not only study modification and immutability. It also
- does null-pointer analysis
- computes preconditions
- tracks instance state of collection objects (like when a set is empty, or not)
- checks for dead code, useless assignments, trivial conditions, etc.
- detects fluent methods, identity methods
- detects singleton classes, utility classes, and extension classes
- enforces finalizer methods
The Manual → is the right place to discover what the analyser can do.