Merge pull request #51 from Curabis/rule/binary-choice-must-be-boolean

[BCQuality] Binary yes/no choices must be Boolean, not Option/Integer

custom/knowledge/style/binary-choice-must-be-boolean.md

@@ -0,0 +1,59 @@
+---
+bc-version: [all]
+domain: style
+keywords: [boolean, option, yes-no, magic-number, variable-typing, field-typing]
+technologies: [al]
+countries: [w1]
+application-area: [all]
+---
+
+# Binary yes/no choices must be typed as Boolean, not Option or Integer
+
+## Description
+
+When a field or variable represents exactly two states — yes/no, on/off,
+active/inactive, blocked/not blocked — it must be typed `Boolean`. Modeling
+that same two-state choice as an `Option`/`Enum` with two members, or as an
+`Integer` with two magic-number values (0/1), adds a layer of indirection a
+reader has to resolve before understanding the code, and it invites a
+three-way branch (`if X = 0 then ... else if X = 1 then ...`) where a simple
+`if X then ...` would do.
+
+This is distinct from a genuine multi-value choice — see
+[[fixed-choice-set-must-use-enum-not-integer]] — where more than two named
+states legitimately call for `Enum`. The line is the state count: exactly
+two mutually exclusive states is a Boolean question, not an enumeration.
+
+## Best Practice
+
+```al
+field(50; Blocked; Boolean)
+{
+}
+
+var
+    IsOverdue: Boolean;
+...
+IsOverdue := DueDate < Today;
+if IsOverdue then
+    ...
+```
+
+## Anti Pattern
+
+```al
+field(50; Status; Option)
+{
+    OptionMembers = Active,Blocked;
+}
+
+var
+    OverdueFlag: Integer; // 0 = No, 1 = Yes
+...
+if OverdueFlag = 1 then
+    ...
+```
+
+An `Option`/`Integer` standing in for a true yes/no forces every caller to
+remember which value means what, and it leaves room for a third, meaningless
+value that a `Boolean` cannot represent.