Cohesion analysis for containers (modules/classes).

Measures how well the members (methods/functions) of a container work together. High cohesion indicates that members are closely related and work toward a common purpose, which is a desirable property in object-oriented design.

Supported Metrics

LCOM (Lack of Cohesion of Methods)

Measures the number of disjoint sets of methods. Lower is better.

• LCOM = 0: Perfect cohesion (all methods share state)
• LCOM > 0: Poor cohesion (methods form disconnected groups)

TCC (Tight Class Cohesion)

Ratio of directly connected method pairs. Range: 0.0-1.0, higher is better.

• TCC = 1.0: All methods directly share state
• TCC > 0.5: Good cohesion
• TCC < 0.3: Poor cohesion

LCC (Loose Class Cohesion)

Ratio of directly or indirectly connected method pairs. Range: 0.0-1.0.

• LCC >= TCC always
• High LCC but low TCC: Methods connected through intermediaries

Algorithm

1. Extract all methods/functions from container
2. For each method, identify which instance variables it accesses
3. Build a connection graph between methods based on shared variables
4. Calculate LCOM (number of disconnected components)
5. Calculate TCC (direct connections / total possible pairs)
6. Calculate LCC (transitive closure / total possible pairs)

Examples

# High cohesion - all methods use shared state
ast = {:container, :class, "BankAccount", %{}, [
  {:function_def, :public, "deposit", ["amount"], %{},
   {:augmented_assignment, :+, {:attribute_access, {:variable, "self"}, "balance"}, {:variable, "amount"}}},
  {:function_def, :public, "withdraw", ["amount"], %{},
   {:augmented_assignment, :-, {:attribute_access, {:variable, "self"}, "balance"}, {:variable, "amount"}}},
  {:function_def, :public, "get_balance", [], %{},
   {:attribute_access, {:variable, "self"}, "balance"}}
]}

doc = Document.new(ast, :python)
{:ok, result} = Cohesion.analyze(doc)

result.lcom           # => 0 (perfect cohesion)
result.tcc            # => 1.0 (all methods connected)
result.assessment     # => :excellent

# Low cohesion - methods don't share state
ast = {:container, :class, "Utilities", %{}, [
  {:function_def, :public, "format_date", ["date"], %{}, ...},
  {:function_def, :public, "calculate_tax", ["amount"], %{}, ...},
  {:function_def, :public, "send_email", ["to", "msg"], %{}, ...}
]}

{:ok, result} = Cohesion.analyze(doc)
result.lcom           # => 3 (three disjoint methods)
result.tcc            # => 0.0 (no shared state)
result.assessment     # => :very_poor