interface.go

     1  // Copyright 2021 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package types
     6  
     7  import (
     8  	"go/ast"
     9  	"go/token"
    10  )
    11  
    12  // ----------------------------------------------------------------------------
    13  // API
    14  
    15  // An Interface represents an interface type.
    16  type Interface struct {
    17  	check     *Checker     // for error reporting; nil once type set is computed
    18  	obj       *TypeName    // type name object defining this interface; or nil (for better error messages)
    19  	methods   []*Func      // ordered list of explicitly declared methods
    20  	embeddeds []Type       // ordered list of explicitly embedded elements
    21  	embedPos  *[]token.Pos // positions of embedded elements; or nil (for error messages) - use pointer to save space
    22  	implicit  bool         // interface is wrapper for type set literal (non-interface T, ~T, or A|B)
    23  	complete  bool         // indicates that obj, methods, and embeddeds are set and type set can be computed
    24  
    25  	tset *_TypeSet // type set described by this interface, computed lazily
    26  }
    27  
    28  // typeSet returns the type set for interface t.
    29  func (t *Interface) typeSet() *_TypeSet { return computeInterfaceTypeSet(t.check, token.NoPos, t) }
    30  
    31  // emptyInterface represents the empty (completed) interface
    32  var emptyInterface = Interface{complete: true, tset: &topTypeSet}
    33  
    34  // NewInterface returns a new interface for the given methods and embedded types.
    35  // NewInterface takes ownership of the provided methods and may modify their types
    36  // by setting missing receivers.
    37  //
    38  // Deprecated: Use NewInterfaceType instead which allows arbitrary embedded types.
    39  func NewInterface(methods []*Func, embeddeds []*Named) *Interface {
    40  	tnames := make([]Type, len(embeddeds))
    41  	for i, t := range embeddeds {
    42  		tnames[i] = t
    43  	}
    44  	return NewInterfaceType(methods, tnames)
    45  }
    46  
    47  // NewInterfaceType returns a new interface for the given methods and embedded
    48  // types. NewInterfaceType takes ownership of the provided methods and may
    49  // modify their types by setting missing receivers.
    50  //
    51  // To avoid race conditions, the interface's type set should be computed before
    52  // concurrent use of the interface, by explicitly calling Complete.
    53  func NewInterfaceType(methods []*Func, embeddeds []Type) *Interface {
    54  	if len(methods) == 0 && len(embeddeds) == 0 {
    55  		return &emptyInterface
    56  	}
    57  
    58  	// set method receivers if necessary
    59  	typ := (*Checker)(nil).newInterface()
    60  	for _, m := range methods {
    61  		if sig := m.typ.(*Signature); sig.recv == nil {
    62  			sig.recv = NewVar(m.pos, m.pkg, "", typ)
    63  		}
    64  	}
    65  
    66  	// sort for API stability
    67  	sortMethods(methods)
    68  
    69  	typ.methods = methods
    70  	typ.embeddeds = embeddeds
    71  	typ.complete = true
    72  
    73  	return typ
    74  }
    75  
    76  // check may be nil
    77  func (check *Checker) newInterface() *Interface {
    78  	typ := &Interface{check: check}
    79  	if check != nil {
    80  		check.needsCleanup(typ)
    81  	}
    82  	return typ
    83  }
    84  
    85  // MarkImplicit marks the interface t as implicit, meaning this interface
    86  // corresponds to a constraint literal such as ~T or A|B without explicit
    87  // interface embedding. MarkImplicit should be called before any concurrent use
    88  // of implicit interfaces.
    89  func (t *Interface) MarkImplicit() {
    90  	t.implicit = true
    91  }
    92  
    93  // NumExplicitMethods returns the number of explicitly declared methods of interface t.
    94  func (t *Interface) NumExplicitMethods() int { return len(t.methods) }
    95  
    96  // ExplicitMethod returns the i'th explicitly declared method of interface t for 0 <= i < t.NumExplicitMethods().
    97  // The methods are ordered by their unique Id.
    98  func (t *Interface) ExplicitMethod(i int) *Func { return t.methods[i] }
    99  
   100  // NumEmbeddeds returns the number of embedded types in interface t.
   101  func (t *Interface) NumEmbeddeds() int { return len(t.embeddeds) }
   102  
   103  // Embedded returns the i'th embedded defined (*Named) type of interface t for 0 <= i < t.NumEmbeddeds().
   104  // The result is nil if the i'th embedded type is not a defined type.
   105  //
   106  // Deprecated: Use EmbeddedType which is not restricted to defined (*Named) types.
   107  func (t *Interface) Embedded(i int) *Named { tname, _ := t.embeddeds[i].(*Named); return tname }
   108  
   109  // EmbeddedType returns the i'th embedded type of interface t for 0 <= i < t.NumEmbeddeds().
   110  func (t *Interface) EmbeddedType(i int) Type { return t.embeddeds[i] }
   111  
   112  // NumMethods returns the total number of methods of interface t.
   113  func (t *Interface) NumMethods() int { return t.typeSet().NumMethods() }
   114  
   115  // Method returns the i'th method of interface t for 0 <= i < t.NumMethods().
   116  // The methods are ordered by their unique Id.
   117  func (t *Interface) Method(i int) *Func { return t.typeSet().Method(i) }
   118  
   119  // Empty reports whether t is the empty interface.
   120  func (t *Interface) Empty() bool { return t.typeSet().IsAll() }
   121  
   122  // IsComparable reports whether each type in interface t's type set is comparable.
   123  func (t *Interface) IsComparable() bool { return t.typeSet().IsComparable(nil) }
   124  
   125  // IsMethodSet reports whether the interface t is fully described by its method
   126  // set.
   127  func (t *Interface) IsMethodSet() bool { return t.typeSet().IsMethodSet() }
   128  
   129  // IsImplicit reports whether the interface t is a wrapper for a type set literal.
   130  func (t *Interface) IsImplicit() bool { return t.implicit }
   131  
   132  // Complete computes the interface's type set. It must be called by users of
   133  // NewInterfaceType and NewInterface after the interface's embedded types are
   134  // fully defined and before using the interface type in any way other than to
   135  // form other types. The interface must not contain duplicate methods or a
   136  // panic occurs. Complete returns the receiver.
   137  //
   138  // Interface types that have been completed are safe for concurrent use.
   139  func (t *Interface) Complete() *Interface {
   140  	if !t.complete {
   141  		t.complete = true
   142  	}
   143  	t.typeSet() // checks if t.tset is already set
   144  	return t
   145  }
   146  
   147  func (t *Interface) Underlying() Type { return t }
   148  func (t *Interface) String() string   { return TypeString(t, nil) }
   149  
   150  // ----------------------------------------------------------------------------
   151  // Implementation
   152  
   153  func (t *Interface) cleanup() {
   154  	t.check = nil
   155  	t.embedPos = nil
   156  }
   157  
   158  func (check *Checker) interfaceType(ityp *Interface, iface *ast.InterfaceType, def *Named) {
   159  	addEmbedded := func(pos token.Pos, typ Type) {
   160  		ityp.embeddeds = append(ityp.embeddeds, typ)
   161  		if ityp.embedPos == nil {
   162  			ityp.embedPos = new([]token.Pos)
   163  		}
   164  		*ityp.embedPos = append(*ityp.embedPos, pos)
   165  	}
   166  
   167  	for _, f := range iface.Methods.List {
   168  		if len(f.Names) == 0 {
   169  			addEmbedded(f.Type.Pos(), parseUnion(check, f.Type))
   170  			continue
   171  		}
   172  		// f.Name != nil
   173  
   174  		// We have a method with name f.Names[0].
   175  		name := f.Names[0]
   176  		if name.Name == "_" {
   177  			check.errorf(name, _BlankIfaceMethod, "invalid method name _")
   178  			continue // ignore
   179  		}
   180  
   181  		typ := check.typ(f.Type)
   182  		sig, _ := typ.(*Signature)
   183  		if sig == nil {
   184  			if typ != Typ[Invalid] {
   185  				check.invalidAST(f.Type, "%s is not a method signature", typ)
   186  			}
   187  			continue // ignore
   188  		}
   189  
   190  		// Always type-check method type parameters but complain if they are not enabled.
   191  		// (This extra check is needed here because interface method signatures don't have
   192  		// a receiver specification.)
   193  		if sig.tparams != nil {
   194  			var at positioner = f.Type
   195  			if ftyp, _ := f.Type.(*ast.FuncType); ftyp != nil && ftyp.TypeParams != nil {
   196  				at = ftyp.TypeParams
   197  			}
   198  			check.errorf(at, _InvalidMethodTypeParams, "methods cannot have type parameters")
   199  		}
   200  
   201  		// use named receiver type if available (for better error messages)
   202  		var recvTyp Type = ityp
   203  		if def != nil {
   204  			recvTyp = def
   205  		}
   206  		sig.recv = NewVar(name.Pos(), check.pkg, "", recvTyp)
   207  
   208  		m := NewFunc(name.Pos(), check.pkg, name.Name, sig)
   209  		check.recordDef(name, m)
   210  		ityp.methods = append(ityp.methods, m)
   211  	}
   212  
   213  	// All methods and embedded elements for this interface are collected;
   214  	// i.e., this interface may be used in a type set computation.
   215  	ityp.complete = true
   216  
   217  	if len(ityp.methods) == 0 && len(ityp.embeddeds) == 0 {
   218  		// empty interface
   219  		ityp.tset = &topTypeSet
   220  		return
   221  	}
   222  
   223  	// sort for API stability
   224  	sortMethods(ityp.methods)
   225  	// (don't sort embeddeds: they must correspond to *embedPos entries)
   226  
   227  	// Compute type set as soon as possible to report any errors.
   228  	// Subsequent uses of type sets will use this computed type
   229  	// set and won't need to pass in a *Checker.
   230  	check.later(func() {
   231  		computeInterfaceTypeSet(check, iface.Pos(), ityp)
   232  	}).describef(iface, "compute type set for %s", ityp)
   233  }
   234
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