The Scala 3 compiler assigns a unique error code to each type of error it can emit. These codes appear in compiler output in the format [E001], [E007], etc.

This section documents each error code with:

• Description — what the error means and when it occurs
• Example — code that triggers the error
• Error output — the actual compiler message you'll see
• Solution — how to fix the problem

scala compile -explain MyFile.scala

Table of Contents

• E001: Empty Catch Block
• E002: Empty Catch And Finally Block
• E003: Deprecated With Operator
• E004: Case Class Missing Param List
• E005: Duplicate Bind
• E006: Missing Ident
• E007: Type Mismatch
• E008: Not A Member
• E009: Early Definitions Not Supported
• E010: Top Level Implicit Class
• E011: Implicit Case Class
• E012: Implicit Class Primary Constructor Arity
• E013: Object May Not Have Self Type
• E014: Tuple Too Long
• E015: Repeated Modifier
• E016: Interpolated String Error
• E017: Unbound Placeholder Parameter
• E018: Illegal Start Simple Expr
• E019: Missing Return Type
• E020: Yield Or Do Expected In For Comprehension
• E021: Proper Definition Not Found
• E022: By Name Parameter Not Supported
• E023: Wrong Number Of Type Args
• E024: Illegal Variable In Pattern Alternative
• E025: Identifier Expected
• E026: Auxiliary Constructor Needs Non-Implicit Parameter
• E027: Varargs Parameter Must Come Last
• E028: Illegal Literal
• E029: Pattern Match Exhaustivity
• E030: Match Case Unreachable
• E031: Sequence Wildcard Pattern Position
• E032: Illegal Start Of Simple Pattern
• E033: Package Duplicate Symbol
• E034: Existential Types No Longer Supported
• E035: Unbound Wildcard Type
• E036: Dangling This In Path
• E037: Overrides Nothing
• E038: Overrides Nothing But Name Exists
• E039: Forward Reference Extends Over Definition
• E040: Expected Token But Found
• E041: Mixed Left And Right Associative Ops
• E042: Cannot Instantiate Abstract Class Or Trait
• E043: Unreducible Application
• E044: Overloaded Or Recursive Method Needs Result Type
• E045: Recursive Value Needs Result Type
• E046: Cyclic Reference Involving
• E047: Cyclic Reference Involving Implicit
• E048: Super Qualifier Must Be Parent
• E049: Ambiguous Reference
• E050: Method Does Not Take Parameters
• E051: Ambiguous Overload
• E052: Reassignment To Val
• E053: Type Does Not Take Parameters
• E054: Parameterized Type Lacks Arguments
• E055: Var Val Parameters May Not Be Call By Name
• E056: Missing Type Parameter For
• E057: Does Not Conform To Bound
• E058: Does Not Conform To Self Type
• E059: Does Not Conform To Self Type Cannot Be Instantiated
• E060: Abstract Member May Not Have Modifier
• E061: Top Level Can't Be Implicit
• E062: Types And Traits Cannot Be Implicit
• E063: Only Classes Can Be Abstract
• E064: Abstract Override Only In Traits
• E065: Traits May Not Be Final
• E066: Native Members May Not Have Implementation
• E067: Only Classes Can Have Declared But Undefined Members
• E068: Cannot Extend AnyVal
• E069: Cannot Have Same Name As
• E070: Value Classes May Not Define Inner Class
• E071: Value Classes May Not Define Non Parameter Field
• E072: Value Classes May Not Define A Secondary Constructor
• E073: Value Classes May Not Contain Initialization
• E074: Value Classes May Not Be Abstract
• E075: Value Classes May Not Be Contained
• E076: Value Classes May Not Wrap Another Value Class
• E077: Value Class Parameter May Not Be A Var
• E078: Value Class Needs Exactly One Val Parameter
• E079: Only Case Class Or Case Object Allowed
• E080: Expected Top Level Def
• E081: Anonymous Function Missing Parameter Type
• E082: Super Calls Not Allowed In Inlineable
• E083: Not A Path
• E084: Wildcard On Type Argument Not Allowed On New
• E085: Function Type Needs Non-Empty Parameter List
• E086: Wrong Number Of Parameters
• E087: Duplicate Private Protected Qualifier
• E088: Expected Start Of Top Level Definition
• E089: Missing Return Type With Return Statement
• E090: No Return From Inlineable
• E091: Return Outside Method Definition
• E092: Unchecked Type Pattern
• E093: Extend Final Class
• E094: Enum Case Definition In Non-Enum Owner
• E095: Expected Type Bound Or Equals
• E096: Class And Companion Name Clash
• E097: Tailrec Not Applicable
• E098: Failure To Eliminate Existential
• E099: Only Functions Can Be Followed By Underscore
• E100: Missing Empty Argument List
• E101: Duplicate Named Type Parameter
• E102: Undefined Named Type Parameter
• E103: Illegal Start of Statement
• E104: Trait Is Expected
• E105: Trait Redefined Final Method From AnyRef
• E106: Package Name Already Defined
• E107: Unapply Invalid Number of Arguments
• E108: Unapply Invalid Return Type
• E109: Static Fields Only Allowed in Objects
• E110: Cyclic Inheritance
• E111: Bad Symbolic Reference
• E112: Unable to Extend Sealed Class
• E113: Symbol Has Unparsable Version Number
• E114: Symbol Changed Semantics In Version
• E115: Unable to Emit Switch
• E116: Missing Companion for Static
• E117: Polymorphic Method Missing Type in Parent
• E118: Params No Inline
• E119: Symbol Is Not a Value
• E120: Double Definition
• E121: Match Case Only Null Warning
• E122: Imported Twice
• E123: Type Test Always Diverges
• E124: Term Member Needs Result Type for Implicit Search
• E125: Class Cannot Extend Enum
• E126: Value Class Parameter May Not Be Call-By-Name
• E127: Not An Extractor
• E128: Member With Same Name As Static
• E129: Pure Expression In Statement Position
• E130: Trait Companion With Mutable Static
• E131: Lazy Static Field
• E132: Static Overriding Non-Static Members
• E133: Overload In Refinement
• E134: No Matching Overload
• E135: Stable Identifier Pattern
• E136: Static Fields Should Precede Non-Static
• E137: Illegal Super Accessor
• E138: Trait Parameter Used As Parent Prefix
• E139: Unknown Named Enclosing Class Or Object
• E140: Illegal Cyclic Type Reference
• E141: Missing Type Parameter In Type App
• E142: Skolem in Inferred
• E143: Erased Types Can Only Be Function Types
• E144: Case Class Missing Non-Implicit Parameter List
• E145: Enumerations Should Not Be Empty
• E146: Illegal Parameter Initialization
• E147: Redundant Modifier
• E148: Typed Case Does Not Explicitly Extend Typed Enum
• E149: Illegal Redefinition Of Standard Kind
• E150: No Extension Method Allowed
• E151: Extension Method Cannot Have Type Parameters
• E152: Extension Can Only Have Defs
• E153: Unexpected Pattern For SummonFrom
• E154: Anonymous Instance Cannot Be Empty
• E155: Type Splice in Val Pattern
• E156: Modifier Not Allowed For Definition
• E157: Cannot Extend Java Enum
• E158: Invalid Reference In ImplicitNotFound Annotation
• E159: Trait May Not Define Native Method
• E160: Java Enum Parent Args
• E161: Already Defined
• E162: Case Class In Inlined Code
• E163: Override Type Mismatch Error
• E164: Override Error
• E165: Matchable Warning
• E166: Cannot Extend Function
• E167: Lossy Widening Constant Conversion
• E168: Implicit Search Too Large
• E169: TargetName On Top-Level Class
• E170: Not Class Type
• E171: Missing Argument
• E172: Missing Implicit Argument
• E173: Cannot Be Accessed
• E174: Inline Given Should Not Be Function
• E175: Value Discarding
• E176: Unused Non-Unit Value
• E177: Constructor Proxy Shadows
• E178: Missing Argument List
• E179: Match Type Scrutinee Cannot Be Higher-Kinded
• E180: Ambiguous Extension Method
• E181: Unqualified Call to AnyRef Method
• E182: Not Constant
• E183: Closure Cannot Have Internal Parameter Dependencies
• E184: Match Type No Cases
• E185: Unimported and Imported
• E186: Implausible Pattern Warning
• E187: Synchronized Call on Boxed Class
• E188: VarArgs Param Cannot Be Given
• E189: Extractor Not Found
• E190: Pure Unit Expression
• E191: Match Type Legacy Pattern
• E192: Unstable Inline Accessor
• E193: Volatile on Val
• E194: Extension Nullified by Member
• E195: Phantom Symbol Not Value
• E196: Context Bound Companion Not Value
• E197: Inlined Anonymous Class Warning
• E198: Unused Symbol
• E199: Tailrec Nested Call
• E200: Final Local Def
• E201: Non-Named Argument in Java Annotation
• E202: Quoted Type Missing
• E203: Deprecated Assignment Syntax
• E204: Deprecated Infix Named Argument Syntax
• E205: Given Search Priority Warning
• E206: Enum May Not Be Value Class
• E207: Illegal Unroll Placement
• E208: Extension Has Default Receiver
• E209: Format Interpolation Error
• E210: Value Class Cannot Extend Alias of AnyVal
• E211: Match Is Not Partial Function
• E212: Only Fully Dependent Applied Constructor Type
• E213: Pointless Applied Constructor Type
• E214: Illegal Context Bounds
• E215: Named Pattern Not Applicable
• E216: Unnecessary .nn
• E217: Erased Not Pure
• E218: Illegal Erased Definition
• E219: Cannot Instantiate Quoted Type Variable
• E220: Default Shadows Given
• E221: Recurse With Default
• E222: Encoded Package Name
• E223: Cannot Be Included in Capture Set
• E224: Override Class
• E225: Infer Union Warning
• E226: Type Parameter Shadows Type
• E227: Private Shadows Type