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Add C07 study pages; regenerate C06 via the shared port script sd/C07: home + Naming Conventions, Internal Documentation, Validation Techniques (21 skill codes), linked from the SD hub. sd/C06 pages regenerated by sat/port-reference-godot-to-wiki.py (marker update; C06-home now generated from the repo README like every other page). Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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# Validation Techniques — GDScript
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**Skill codes on this page**
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| Code | Level | Skill |
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|---|---|---|
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| C713 | 1–2 | identifies input data for validation |
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| C723 | 3–4 | existence checking |
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| C724 | 3–4 | type checking |
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| C725 | 3–4 | range checking |
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| C735 | 5–6 | two of the three checks |
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| C745 | 7–8 | all three checks |
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| C753 ✍️ | 9–10 | ALL input data, plus reasonableness and completeness |
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**Definition.** *Validation* checks the reasonableness of data inputs, while the program runs. It is not testing (testing happens to the finished program; validation happens to every input, every run). The three named checks: **existence** (was anything entered?), **type** (is it the right kind of value?), **range** (is it within acceptable limits?).
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**This ladder is not a checklist.** The individual checks are separate codes only at level 3–4. Above that, single codes stand for the *combination*: C735 = two checks working, C745 = all three, C753 = all inputs plus reasonableness and completeness. Consistency qualifiers decide the band: *some inconsistencies* (5–6) → *minor* (7–8) → *none* (9–10).
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**In the validation** Part B you add existence/type/range checks to the picked feature's real inputs, label them as you go, and **run a test to show a check actually fires** — a validation that never catches a bad value is scenery.
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## C713 — Identify the inputs
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Level 1–2 is a written list of what needs validating:
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```gdscript
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# C713 — inputs to validate in this feature:
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# team name — NameField (LineEdit), free text
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# zone — ZoneSpinBox (SpinBox), whole number
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# top-up — TopUpField (LineEdit), dollars and cents
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```
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**Earns the tick:** every user-facing input of the picked feature named. (Choosing constrained controls — a SpinBox can't receive letters — is good design, but the codes below want checks *in code*.)
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## C723 — Existence check
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**Definition.** A test to see if a value has been entered as input or not.
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```gdscript
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# club-ladder — app.gd
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func add_team(raw_name: String) -> void:
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var team_name := raw_name.strip_edges()
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if team_name == "": # C723 — existence: nothing entered
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message_label.text = "Type a team name first."
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return
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```
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Note the real-world details worth copying: `strip_edges()` first (spaces are not a name), and an error message that says **what to do**, not just "invalid".
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## C724 — Type check
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**Definition.** A test to see if a value is of the specified data type or structure.
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GDScript's idioms — check *before* converting, or the conversion itself is the crash:
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```gdscript
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# C724 — type: is the text actually a number?
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if not $TopUpField.text.is_valid_float():
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$MessageLabel.text = "Enter an amount in dollars, like 10.50"
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return
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var amount := float($TopUpField.text)
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```
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`String.is_valid_int()` and `is_valid_float()` are the workhorses. The `is` keyword type-checks objects — real use in tile-matching-game: `if child is Card:` (`board.gd`).
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## C725 — Range check
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**Definition.** Tests to see if a value is within a given range of acceptable values.
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```gdscript
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# C725 — range: zones only run 1..3, amounts have a ceiling
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if zone < 1 or zone > MAX_ZONE:
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$MessageLabel.text = "Zone must be 1 to %d" % MAX_ZONE
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return
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if amount <= 0.0 or amount > MAX_TOP_UP:
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$MessageLabel.text = "Top-up must be between $0.01 and $%.2f" % MAX_TOP_UP
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return
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```
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The limits are **named constants** (`MAX_ZONE`, `MAX_TOP_UP`) — that's C7-1 working for C7-3. Clamping (`maxi(1, column_count)` in club-ladder's `board.gd`) is the accept-and-correct cousin of reject-and-message; for user input, prefer the message — silent correction hides the user's mistake from them.
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## C735 and C745 — The checks working together
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One validated input, all three checks, in the order that cannot crash — existence, then type, then range:
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```gdscript
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# C745 — full validation of the top-up amount (existence → type → range)
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func validate_top_up(raw: String) -> String:
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var text := raw.strip_edges()
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if text == "": # C723 — existence
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return "Enter an amount first."
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if not text.is_valid_float(): # C724 — type
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return "Enter a number, like 10.50"
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var amount := float(text)
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if amount <= 0.0 or amount > MAX_TOP_UP: # C725 — range
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return "Amount must be between $0.01 and $%.2f" % MAX_TOP_UP
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return "" # empty string = valid
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```
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C735 (5–6) is two of these working on real inputs; C745 (7–8) is all three, with at most *minor* inconsistencies. **Error messages are part of the standard** — "Must be between 8 and 72 in length" beats "Invalid input" because it tells the user how to fix it (that Discord message was the class's best-in-show in the Validation Detective activity).
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## C753 — All inputs, plus reasonableness and completeness ✍️
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Level 9–10 widens the lens from single fields to the **whole data set**:
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- **All relevant inputs** validated — not just the easy one.
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- **Completeness** — is anything missing? Real example: `deck.gd` skips half-empty CSV rows with `if row.size() < 2: continue` (tile-matching-game).
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- **Reasonableness** — can these values be true *together*? The model is club-ladder's cross-check:
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```gdscript
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# club-ladder — app.gd
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## In a competition where teams play each other, one team's win is always # C753 ✍️
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## another's loss — so total wins must equal total losses. Worth saying on
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## screen rather than quietly showing figures that cannot be true.
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func totals_warning() -> String:
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if total_wins == total_losses:
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return ""
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return "Check your data: %d wins recorded, but %d losses." % [total_wins, total_losses]
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```
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**Earns the tick:** every input covered, a completeness check on incoming records, at least one reasonableness rule that crosses fields — and (✍️) the rule *written down*: work out what rules **your** data has to obey, and say so in a comment.
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**Then prove it fires.** End the validation task by entering a bad value and showing the message appear — the package script asks for exactly this test run.
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## Check Your Understanding
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1. Name the three validation checks and their level 3–4 codes.
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>| ### Answer
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>| Existence C723, type C724, range C725.
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2. Why are C735 and C745 single codes rather than lists of checks?
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>| ### Answer
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>| Above level 3–4 the descriptor rewards the *combination* — two checks working (C735), then all three (C745) — with consistency qualifiers deciding the band.
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3. What makes "Must be between 8 and 72 in length" a better error message than "Invalid input"?
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>| ### Answer
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>| It tells the user exactly how to fix the problem — specific beats generic.
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4. Give an example of a reasonableness check (C753).
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>| ### Answer
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>| A cross-field rule — e.g. club-ladder's "total wins must equal total losses"; values that are individually fine but cannot be true together.