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Nanaloveyuki
77 lines
2.1 KiB
Markdown
77 lines
2.1 KiB
Markdown
---
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name: field-with-value
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group: api
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category: record
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update-time: 20260613
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description: Return a copy of a field with a replaced value while preserving the key.
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key-word:
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- field
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- value
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- transform
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- public
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---
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## Field-with-value
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Return a copy of a `Field` with a different `value`. This helper is the narrowest way to rewrite one field value while preserving the existing key.
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### Interface
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```moonbit
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pub fn Field::with_value(self : Field, value : String) -> Field {}
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```
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#### input
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- `self : Field` - Base field whose value should be replaced.
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- `value : String` - New value text for the returned field.
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#### output
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- `Field` - New field value carrying the updated value.
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### Explanation
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Detailed rules explaining key parameters and behaviors
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- This helper returns a new field value instead of mutating the original one.
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- Only the `value` part is replaced.
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- The original `key` is preserved exactly.
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- This is useful for redaction, normalization, or tests that need one adjusted field value without rebuilding the key manually.
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### How to Use
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Here are some specific examples provided.
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#### When Need To Redact One Existing Field Value
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When the field key should stay the same but the value should be hidden:
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```moonbit
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let user = field("user", "alice")
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let redacted = user.with_value("***")
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```
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In this example, the returned field keeps the same key while changing only the visible value.
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#### When Need To Rewrite A Field In Test Data
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When one field should be adapted without reconstructing the key by hand:
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```moonbit
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let region = field("region", "cn").with_value("eu")
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```
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In this example, the helper keeps the transformation local to one field value.
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### Error Case
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e.g.:
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- If `value` is empty, the returned field is still valid and simply carries an empty string value.
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- If the key should also change, constructing a new field with `field(...)` is clearer than chaining this helper.
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### Notes
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1. Use this helper when the key should stay stable and only the value should change.
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2. It is especially useful for redaction-style value updates in tests or adapters.
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