ek9_extract_trait

Appends a new 'defines trait' block declaring the chosen methods as abstract, adds 'with trait of <Name>' to the class header and 'override' to each method; answers status, edits[] and summary, a non-extractable member as conflicts[] (member-not-extractable-to-trait).

Category: Editor · Compare: Extract Interface (IntelliJ / Eclipse)

When to use it

'Pull validate out of CustomerOrder into a Validatable trait' is one call with symbol:'CustomerOrder', members:['validate'] and name:'Validatable'.

When not to use it

Extracting a CODE BLOCK into a method on the SAME class, not a method into a trait - use ek9_extract_method.
The trait already EXISTS and you want to add its implementation on a class that declares it - use ek9_implement_methods.
The class should DELEGATE to a trait via a field ('with trait of T by field'), not BE the impl - use ek9_generate_delegation.
Promoting a method to a SUPERCLASS rather than a separate trait - use ek9_pull_up.
The member is private/protected - traits are public-only (E07270); raise visibility first with ek9_change_visibility, or keep it on the class.

Details

Class targets only - records/components/functions error. A named method that is not a public, non-operator method of the class (not found, private/protected, an operator, or a field per E07075) returns status:'conflicts' (kind 'member-not-extractable-to-trait'), not an error. 'override' is always prepended on the class per E05120 - no opt-out; V1 appends the new 'defines trait' block to the SAME file, declaring the methods 'as abstract' (the class keeps its bodies).

Arguments

Argument	Type	Required	What it is
`file`	string		The EK9 source file - OPTIONAL when symbol is a construct name; required to anchor on a member or a use site.
`line`	integer		1-based line of the declaration or a reference - OMIT it and pass symbol:'<name>' to let the tool find the line (a model counting lines in a file miscounts); if you do count, use `ek9_read_file`(lineNumbers:true).
`members`	array of string	yes	Names of PUBLIC methods on the class to extract into the trait.
`name`	string	yes	The new trait's identifier (PascalCase by convention). Must not already exist in the file.
`symbol`	string	yes	The class whose methods move to the trait - a bare name ('CustomerOrder') finds its file and declaration workspace-wide; 'mod::CustomerOrder' when the name is declared in two modules.

It also takes the arguments every tool takes.

Recorded calls

Real calls, recorded against small projects and checked on every build - a changed answer fails it. 3 of the 4 recorded are shown.

Non class error

Request

{
  "file" : "rec.ek9",
  "line" : 6,
  "methods" : [ "x" ],
  "traitName" : "HasPoint"
}

Response

{
  "conflicts" : [ ],
  "edits" : [ ],
  "error" : {
    "message" : "'Point' is a record — extract-trait targets classes only"
  },
  "meta" : {
    "serverMs" : "<timing>"
  },
  "status" : "error",
  "summary" : "'Point' is a record — extract-trait targets classes only",
  "wouldBeDiagnostics" : [ ],
  "written" : false
}

Name collision conflict

Request

{
  "file" : "payment.ek9",
  "line" : 6,
  "methods" : [ "process" ],
  "traitName" : "PaymentProcessor"
}

Response

{
  "conflicts" : [ {
    "kind" : "name-collision-with-existing-trait",
    "message" : "Pick a different trait name — 'PaymentProcessor' is already declared"
  } ],
  "edits" : [ ],
  "meta" : {
    "serverMs" : "<timing>"
  },
  "risk" : {
    "crossesModuleBoundary" : false,
    "estimatedSeverity" : "trivial",
    "fileCount" : 0,
    "lineCount" : 0,
    "touchesPublicApi" : false,
    "touchesTests" : false
  },
  "status" : "conflicts",
  "summary" : "A construct named 'PaymentProcessor' already exists in this file",
  "workspaceHash" : "<workspace-hash>",
  "wouldBeDiagnostics" : [ ],
  "written" : false
}

Apply creates trait

Request

{
  "file" : "payment.ek9",
  "line" : 6,
  "methods" : [ "process", "refund" ],
  "traitName" : "Payment"
}

Response

{
  "conflicts" : [ ],
  "edits" : [ {
    "after" : "\n  defines trait\n    Payment\n\n      process() as abstract\n        -> amount as Float\n        <- rtn as Boolean?\n\n      refund() as abstract\n        -> amount as Float\n        <- rtn as Boolean?\n",
    "endLine" : 14,
    "file" : "payment.ek9",
    "startLine" : 14,
    "type" : "insert"
  }, {
    "after" : "    PaymentProcessor with trait of Payment",
    "before" : "    PaymentProcessor",
    "endLine" : 6,
    "file" : "payment.ek9",
    "startLine" : 6,
    "type" : "replace"
  }, {
    "after" : "      override process()",
    "before" : "      process()",
    "endLine" : 7,
    "file" : "payment.ek9",
    "startLine" : 7,
    "type" : "replace"
  }, {
    "after" : "      override refund()",
...

Cut short here: 23 more lines. The whole recorded call.

When to use it

When not to use it

Details

Arguments

Recorded calls

Non class error

Name collision conflict

Apply creates trait

See also