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JDT Core Programmer Guide/ECJ/Bindings
Contents
Main Kinds of Bindings
See the type hierarchy of org.eclipse.jdt.internal.compiler.lookup.Binding
. This class also declares constants which define possible answers from Binding.kind()
.
- One reason why kinds are or-able bits: a NameReference can use an int as bitset to encode if it can legally resolve to a variable, or a type, or both, where variable can be either a field or a local.
As a special type, UnresolvedReferenceBinding
is a placeholder for a not-yet resolved ReferenceBinding. Resolving an UnresolvedReferenceBinding will update its holder, too. This type is used in signatures of members of BinaryTypeBinding
to avoid the need to read all class file dependencies. By construction, types in class files are always represented by their fully qualified name, so lookup of these types does not require any context.
Another group of bindings is synthesized by the compiler from thin air, see #Synthetic Bindings.
General rules for Bindings
No null
In constrast to AST, where null
is typically a legal field value, bindings typically use constants of the NO_*
family to denote "nothing here". null
would typically indicate "not initialized".
Comparison
Since bindings are unique by construction, it would normally be OK to compare bindings using ==
or !=
. Specifically with the introduction of TYPE_USE annotations, even the same type can be represented by different bindings to account for attached annotations. For that reason, specific comparison methods have been added, which should be used throughout:
-
TypeBinding.equalsEquals()
-
TypeBinding.notEquals()
These methods ignore difference only in annotations. Those rare cases where annotation difference should indeed be considered have to be marked in source with //$IDENTITY-COMPARISON$
, to suppress a warning implemented specifically for the compiler's own sake.
Internally, each TypeBinding
has an id
. Low values correspond to well-known types (see TypeIds
), while higher values are allocated dynamically. Ids are interesting as the family of all type bindings derived from the same original share the same id. Ids also simplify checks for well-known types.
Non-Uniqueness
Contrary to the general rule, a number of reasons exist, why the same source entity can be represented by several distinct bindings:
- When the same package exists in several modules, we create one
PackageBinding
per module, plus aSplitPackageBinding
to combine the slices into one. The current strategy concerning SplitPackageBinding was developed via bug 547181 which has a lot of explanations. - From a generic type (
SourceTypeBinding
orBinaryTypeBinding
) a number of parameterizations can be created usingParameterizedTypeBinding
.- For each contained
MethodBinding
aParameterizedMethodBinding
is created to carry the instantiation of type variables. - For each contained
FieldBinding
aParameterizedFieldBinding
is created to carry the instantiation of type variables.
- For each contained
- From a generic method (
MethodBinding
) a number of parameterizations can be created usingParameterizedGenericMethodBinding
. While ParameterizedMethodBinding captures type variables of the declaring class, ParameterizedGenericMethodBinding captures type variables declared by the method itself. - From each
TypeBinding
a number of "clones" (of the same type) can be created with different sets of TYPE_USE annotations. Indeed, methodTypeBinding.clone()
is used for this process, andTypeBinding.prototype()
will answer the original from which an annotated type was cloned. - From each
WildcardBinding
a number ofCaptureBinding
can be created, but that's not of ECJ's invention, but specified in JLS.
When comparing bindings, it is sometimes necessary, to explicitly strip a wrapper binding using one of these methods:
-
TypeBinding.original()
strips annotations, and erases parameterized, raw and array types -
TypeBinding.erasure()
full erasure (no type arguments), but may or may not retain annotations -
TypeBinding.unannotated()
strips annotations only -
TypeBinding.actualType()
answers the erasure from ParameterizedTypeBinding and WildcardBinding,null
otherwise -
ParameterizedTypeBinding.genericType()
: likeactualType()
but performes lazy resolving of UnresolvedReferenceBinding -
MethodBinding.genericMethod()
: strips instantiation of a method's own type variables -
MethodBinding.original()
: strips any parameterization -
MethodBinding.shallowOriginal()
: strips instantiation of a method's own type variables, but leaves instantiations of class parameters in place (unclear if different from genericMethod()).
Parameterization and nesting
A plain method inside a ParameterizedType will be represented by a ParameterizedMethodBinding. But what about a nested type inside a generic outer type?
- If the nested type is static, any type parameters from its outer class are irrelevant for the nested type, as it cannot access them without an outer instance.
- If the nested type is non-static, reference to this type are represented by a ParameterizedTypeBinding even if the nested type itself declares no type parameters, because here the nested type can refer to type variables of the enclosing type & instance (this was wrong prior to bug 460491).
Flag vectors
-
tagBits
(TypeBinding,MethodBinding,VariableBinding): set of bits as declared inTagBits
- Is*: fine grained classification of a binding
- Begin*, End*: pairs of flags that indicate when a given processing step is active / complete (used to avoid re-entrance / recursion).
- AreFieldsComplete, AreFieldsSorted, AreMethodsComplete, AreMethodsSorted: describes that status of arrays
fields
andmethods
- Has*: various diagnostics
- Annotation*: marks when a given annotation has been applied to the element.
-
extendedTagBits
(TypeBinding): overflow from tagBits, constants are inExtendedTagBits
.
New bits should preferrably be allocated here, rather than the crowded TagBits. -
typeBits
(ReferenceBinding): classification of types, constants inTypeIds
:- classification of resources (below
Closeable
), see Analysis->Black lists / white lists - BitUninitialized
- BitUninternedType: classify JDT's own types
TypeBinding
(compiler) andITypeBinding
DOM as not suitable for reference comparison (==
,!=
), unless documented$IDENTITY-COMPARISON
. - Bit*Null*Annotation: detect annotation types, configured for use by ECJ's annotation based null analysis.
- BitMap, BitCollection, BitList: mark types which have methods with well-known problems (see UnlikelyArgumentCheck).
- classification of resources (below
Synthetic Bindings
TBC
Other classes in the lookup package
the structure of this section should be improved.
Constants
- TagBits - big bag of flags in bitset
tagBits
, see #Flag Vectors - ExtendedTagBits, see #Flag Vectors
- ExtraCompilerModifiers - will appear in fields
modifier
but are never found in .class files - ProblemReasons - constants used in Problem*Binding
- TypeConstants - not only type, also well-known method names etc
- TypeIds - integer constants relating to types
Management of variants of a type binding
- TypeSystem
- AnnotatableTypeSystem
Type Inference
Here be draggons, read [JLS §18] first.
- InferenceContext18 (variant InferenceContext is used only below 1.8 - not really maintained any more)
- BoundSet
- InferenceVariable
- ReductionResult
- TypeBound
- ConstraintFormula
- ConstraintExpressionFormula
- ConstraintExceptionFormula
- ConstraintTypeFormula
- InferenceSubstitution
Scopes
see JDT Core Programmer Guide/ECJ/Lookups#Scopes
Reading .class files
- SignatureWrapper: incremental interpretation of a signature in binary format
Visiting
- TypeBindingVisitor
Null Annotations
- ImplicitNullAnnotationVerifier: check if method overriding is valid wrt null annotations
- ParameterNonNullDefaultProvider: implements the effect of @NonNullByDefault on method parameters
- ExternalAnnotationSuperimposer: See hierarchy of
org.eclipse.jdt.internal.compiler.env.ITypeAnnotationWalker
.
Post-resolution computations
- MethodVerifier
- MethodVerifier15