pub enum ValidationType {
Show 54 variants
Email,
Url,
Uuid,
Cuid,
Cuid2,
NanoId,
Ulid,
Regex(String),
MinLength(usize),
MaxLength(usize),
Length {
min: usize,
max: usize,
},
StartsWith(String),
EndsWith(String),
Contains(String),
Alpha,
Alphanumeric,
Lowercase,
Uppercase,
Trim,
NoWhitespace,
Ip,
Ipv4,
Ipv6,
CreditCard,
Phone,
Slug,
Hex,
Base64,
Json,
Min(f64),
Max(f64),
Range {
min: f64,
max: f64,
},
Positive,
Negative,
NonNegative,
NonPositive,
Integer,
MultipleOf(f64),
Finite,
MinItems(usize),
MaxItems(usize),
Items {
min: usize,
max: usize,
},
Unique,
NonEmpty,
Past,
Future,
PastOrPresent,
FutureOrPresent,
After(String),
Before(String),
Required,
NotEmpty,
OneOf(Vec<ValidationValue>),
Custom(String),
}Expand description
Types of validation rules.
Variants§
Valid email format.
Url
Valid URL format.
Uuid
Valid UUID format (v1-v5).
Cuid
Valid CUID format.
Cuid2
Valid CUID2 format.
NanoId
Valid NanoId format.
Ulid
Valid ULID format.
Regex(String)
Matches regex pattern.
MinLength(usize)
Minimum string length.
MaxLength(usize)
Maximum string length.
Length
String length range.
StartsWith(String)
String starts with prefix.
EndsWith(String)
String ends with suffix.
Contains(String)
String contains substring.
Alpha
Only alphabetic characters.
Alphanumeric
Only alphanumeric characters.
Lowercase
Only lowercase characters.
Uppercase
Only uppercase characters.
Trim
Trimmed (no leading/trailing whitespace).
NoWhitespace
No whitespace characters.
Ip
Valid IP address (v4 or v6).
Ipv4
Valid IPv4 address.
Ipv6
Valid IPv6 address.
CreditCard
Valid credit card number.
Phone
Valid phone number format.
Slug
URL-safe slug format.
Hex
Valid hexadecimal string.
Base64
Valid base64 string.
Json
Valid JSON string.
Min(f64)
Minimum value.
Max(f64)
Maximum value.
Range
Value within range (inclusive).
Positive
Value > 0.
Negative
Value < 0.
NonNegative
Value >= 0.
NonPositive
Value <= 0.
Integer
Must be integer (no decimal).
MultipleOf(f64)
Value is multiple of n.
Finite
Must be finite (not Infinity/NaN).
MinItems(usize)
Minimum array length.
MaxItems(usize)
Maximum array length.
Items
Array length range.
Unique
All items must be unique.
NonEmpty
Array must have at least one item.
Past
Date must be in the past.
Future
Date must be in the future.
PastOrPresent
Date must be past or present.
FutureOrPresent
Date must be future or present.
After(String)
Date must be after specified date.
Before(String)
Date must be before specified date.
Required
Field must not be null (for optional fields).
NotEmpty
Field must not be empty.
OneOf(Vec<ValidationValue>)
Value must be one of the specified values.
Custom(String)
Use a custom validator function.
Implementations§
Source§impl ValidationType
impl ValidationType
Sourcepub fn default_message(&self, field_name: &str) -> String
pub fn default_message(&self, field_name: &str) -> String
Get the default error message for this validation type.
Sourcepub fn is_string_rule(&self) -> bool
pub fn is_string_rule(&self) -> bool
Check if this rule applies to strings.
Sourcepub fn is_id_format_rule(&self) -> bool
pub fn is_id_format_rule(&self) -> bool
Check if this rule validates an identifier format (UUID, CUID, etc.).
Sourcepub fn is_numeric_rule(&self) -> bool
pub fn is_numeric_rule(&self) -> bool
Check if this rule applies to numbers.
Sourcepub fn is_array_rule(&self) -> bool
pub fn is_array_rule(&self) -> bool
Check if this rule applies to arrays.
Sourcepub fn is_date_rule(&self) -> bool
pub fn is_date_rule(&self) -> bool
Check if this rule applies to dates.
Sourcepub fn validator_name(&self) -> &'static str
pub fn validator_name(&self) -> &'static str
Get the validator name (for code generation).
Trait Implementations§
Source§impl Clone for ValidationType
impl Clone for ValidationType
Source§fn clone(&self) -> ValidationType
fn clone(&self) -> ValidationType
1.0.0 (const: unstable) · Source§fn clone_from(&mut self, source: &Self)
fn clone_from(&mut self, source: &Self)
source. Read moreSource§impl Debug for ValidationType
impl Debug for ValidationType
Source§impl<'de> Deserialize<'de> for ValidationType
impl<'de> Deserialize<'de> for ValidationType
Source§fn deserialize<__D>(
__deserializer: __D,
) -> Result<ValidationType, <__D as Deserializer<'de>>::Error>where
__D: Deserializer<'de>,
fn deserialize<__D>(
__deserializer: __D,
) -> Result<ValidationType, <__D as Deserializer<'de>>::Error>where
__D: Deserializer<'de>,
Source§impl PartialEq for ValidationType
impl PartialEq for ValidationType
Source§impl Serialize for ValidationType
impl Serialize for ValidationType
Source§fn serialize<__S>(
&self,
__serializer: __S,
) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error>where
__S: Serializer,
fn serialize<__S>(
&self,
__serializer: __S,
) -> Result<<__S as Serializer>::Ok, <__S as Serializer>::Error>where
__S: Serializer,
impl StructuralPartialEq for ValidationType
Auto Trait Implementations§
impl Freeze for ValidationType
impl RefUnwindSafe for ValidationType
impl Send for ValidationType
impl Sync for ValidationType
impl Unpin for ValidationType
impl UnsafeUnpin for ValidationType
impl UnwindSafe for ValidationType
Blanket Implementations§
impl<T> Allocation for T
Source§impl<T> BorrowMut<T> for Twhere
T: ?Sized,
impl<T> BorrowMut<T> for Twhere
T: ?Sized,
Source§fn borrow_mut(&mut self) -> &mut T
fn borrow_mut(&mut self) -> &mut T
Source§impl<T> CloneToUninit for Twhere
T: Clone,
impl<T> CloneToUninit for Twhere
T: Clone,
impl<T> DeserializeOwned for Twhere
T: for<'de> Deserialize<'de>,
Source§impl<T> FmtForward for T
impl<T> FmtForward for T
Source§fn fmt_binary(self) -> FmtBinary<Self>where
Self: Binary,
fn fmt_binary(self) -> FmtBinary<Self>where
Self: Binary,
self to use its Binary implementation when Debug-formatted.Source§fn fmt_display(self) -> FmtDisplay<Self>where
Self: Display,
fn fmt_display(self) -> FmtDisplay<Self>where
Self: Display,
self to use its Display implementation when
Debug-formatted.Source§fn fmt_lower_exp(self) -> FmtLowerExp<Self>where
Self: LowerExp,
fn fmt_lower_exp(self) -> FmtLowerExp<Self>where
Self: LowerExp,
self to use its LowerExp implementation when
Debug-formatted.Source§fn fmt_lower_hex(self) -> FmtLowerHex<Self>where
Self: LowerHex,
fn fmt_lower_hex(self) -> FmtLowerHex<Self>where
Self: LowerHex,
self to use its LowerHex implementation when
Debug-formatted.Source§fn fmt_octal(self) -> FmtOctal<Self>where
Self: Octal,
fn fmt_octal(self) -> FmtOctal<Self>where
Self: Octal,
self to use its Octal implementation when Debug-formatted.Source§fn fmt_pointer(self) -> FmtPointer<Self>where
Self: Pointer,
fn fmt_pointer(self) -> FmtPointer<Self>where
Self: Pointer,
self to use its Pointer implementation when
Debug-formatted.Source§fn fmt_upper_exp(self) -> FmtUpperExp<Self>where
Self: UpperExp,
fn fmt_upper_exp(self) -> FmtUpperExp<Self>where
Self: UpperExp,
self to use its UpperExp implementation when
Debug-formatted.Source§fn fmt_upper_hex(self) -> FmtUpperHex<Self>where
Self: UpperHex,
fn fmt_upper_hex(self) -> FmtUpperHex<Self>where
Self: UpperHex,
self to use its UpperHex implementation when
Debug-formatted.Source§impl<T> FromDuckDbRow for Twhere
T: DeserializeOwned,
impl<T> FromDuckDbRow for Twhere
T: DeserializeOwned,
Source§impl<T> FromScyllaRow for Twhere
T: DeserializeOwned,
impl<T> FromScyllaRow for Twhere
T: DeserializeOwned,
Source§impl<T> Instrument for T
impl<T> Instrument for T
Source§fn instrument(self, span: Span) -> Instrumented<Self>
fn instrument(self, span: Span) -> Instrumented<Self>
Source§fn in_current_span(self) -> Instrumented<Self>
fn in_current_span(self) -> Instrumented<Self>
Source§impl<T> IntoEither for T
impl<T> IntoEither for T
Source§fn into_either(self, into_left: bool) -> Either<Self, Self>
fn into_either(self, into_left: bool) -> Either<Self, Self>
self into a Left variant of Either<Self, Self>
if into_left is true.
Converts self into a Right variant of Either<Self, Self>
otherwise. Read moreSource§fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
fn into_either_with<F>(self, into_left: F) -> Either<Self, Self>
self into a Left variant of Either<Self, Self>
if into_left(&self) returns true.
Converts self into a Right variant of Either<Self, Self>
otherwise. Read moreSource§impl<D> OwoColorize for D
impl<D> OwoColorize for D
Source§fn fg<C>(&self) -> FgColorDisplay<'_, C, Self>where
C: Color,
fn fg<C>(&self) -> FgColorDisplay<'_, C, Self>where
C: Color,
Source§fn bg<C>(&self) -> BgColorDisplay<'_, C, Self>where
C: Color,
fn bg<C>(&self) -> BgColorDisplay<'_, C, Self>where
C: Color,
Source§fn black(&self) -> FgColorDisplay<'_, Black, Self>
fn black(&self) -> FgColorDisplay<'_, Black, Self>
Source§fn on_black(&self) -> BgColorDisplay<'_, Black, Self>
fn on_black(&self) -> BgColorDisplay<'_, Black, Self>
Source§fn red(&self) -> FgColorDisplay<'_, Red, Self>
fn red(&self) -> FgColorDisplay<'_, Red, Self>
Source§fn on_red(&self) -> BgColorDisplay<'_, Red, Self>
fn on_red(&self) -> BgColorDisplay<'_, Red, Self>
Source§fn green(&self) -> FgColorDisplay<'_, Green, Self>
fn green(&self) -> FgColorDisplay<'_, Green, Self>
Source§fn on_green(&self) -> BgColorDisplay<'_, Green, Self>
fn on_green(&self) -> BgColorDisplay<'_, Green, Self>
Source§fn yellow(&self) -> FgColorDisplay<'_, Yellow, Self>
fn yellow(&self) -> FgColorDisplay<'_, Yellow, Self>
Source§fn on_yellow(&self) -> BgColorDisplay<'_, Yellow, Self>
fn on_yellow(&self) -> BgColorDisplay<'_, Yellow, Self>
Source§fn blue(&self) -> FgColorDisplay<'_, Blue, Self>
fn blue(&self) -> FgColorDisplay<'_, Blue, Self>
Source§fn on_blue(&self) -> BgColorDisplay<'_, Blue, Self>
fn on_blue(&self) -> BgColorDisplay<'_, Blue, Self>
Source§fn magenta(&self) -> FgColorDisplay<'_, Magenta, Self>
fn magenta(&self) -> FgColorDisplay<'_, Magenta, Self>
Source§fn on_magenta(&self) -> BgColorDisplay<'_, Magenta, Self>
fn on_magenta(&self) -> BgColorDisplay<'_, Magenta, Self>
Source§fn purple(&self) -> FgColorDisplay<'_, Magenta, Self>
fn purple(&self) -> FgColorDisplay<'_, Magenta, Self>
Source§fn on_purple(&self) -> BgColorDisplay<'_, Magenta, Self>
fn on_purple(&self) -> BgColorDisplay<'_, Magenta, Self>
Source§fn cyan(&self) -> FgColorDisplay<'_, Cyan, Self>
fn cyan(&self) -> FgColorDisplay<'_, Cyan, Self>
Source§fn on_cyan(&self) -> BgColorDisplay<'_, Cyan, Self>
fn on_cyan(&self) -> BgColorDisplay<'_, Cyan, Self>
Source§fn white(&self) -> FgColorDisplay<'_, White, Self>
fn white(&self) -> FgColorDisplay<'_, White, Self>
Source§fn on_white(&self) -> BgColorDisplay<'_, White, Self>
fn on_white(&self) -> BgColorDisplay<'_, White, Self>
Source§fn default_color(&self) -> FgColorDisplay<'_, Default, Self>
fn default_color(&self) -> FgColorDisplay<'_, Default, Self>
Source§fn on_default_color(&self) -> BgColorDisplay<'_, Default, Self>
fn on_default_color(&self) -> BgColorDisplay<'_, Default, Self>
Source§fn bright_black(&self) -> FgColorDisplay<'_, BrightBlack, Self>
fn bright_black(&self) -> FgColorDisplay<'_, BrightBlack, Self>
Source§fn on_bright_black(&self) -> BgColorDisplay<'_, BrightBlack, Self>
fn on_bright_black(&self) -> BgColorDisplay<'_, BrightBlack, Self>
Source§fn bright_red(&self) -> FgColorDisplay<'_, BrightRed, Self>
fn bright_red(&self) -> FgColorDisplay<'_, BrightRed, Self>
Source§fn on_bright_red(&self) -> BgColorDisplay<'_, BrightRed, Self>
fn on_bright_red(&self) -> BgColorDisplay<'_, BrightRed, Self>
Source§fn bright_green(&self) -> FgColorDisplay<'_, BrightGreen, Self>
fn bright_green(&self) -> FgColorDisplay<'_, BrightGreen, Self>
Source§fn on_bright_green(&self) -> BgColorDisplay<'_, BrightGreen, Self>
fn on_bright_green(&self) -> BgColorDisplay<'_, BrightGreen, Self>
Source§fn bright_yellow(&self) -> FgColorDisplay<'_, BrightYellow, Self>
fn bright_yellow(&self) -> FgColorDisplay<'_, BrightYellow, Self>
Source§fn on_bright_yellow(&self) -> BgColorDisplay<'_, BrightYellow, Self>
fn on_bright_yellow(&self) -> BgColorDisplay<'_, BrightYellow, Self>
Source§fn bright_blue(&self) -> FgColorDisplay<'_, BrightBlue, Self>
fn bright_blue(&self) -> FgColorDisplay<'_, BrightBlue, Self>
Source§fn on_bright_blue(&self) -> BgColorDisplay<'_, BrightBlue, Self>
fn on_bright_blue(&self) -> BgColorDisplay<'_, BrightBlue, Self>
Source§fn bright_magenta(&self) -> FgColorDisplay<'_, BrightMagenta, Self>
fn bright_magenta(&self) -> FgColorDisplay<'_, BrightMagenta, Self>
Source§fn on_bright_magenta(&self) -> BgColorDisplay<'_, BrightMagenta, Self>
fn on_bright_magenta(&self) -> BgColorDisplay<'_, BrightMagenta, Self>
Source§fn bright_purple(&self) -> FgColorDisplay<'_, BrightMagenta, Self>
fn bright_purple(&self) -> FgColorDisplay<'_, BrightMagenta, Self>
Source§fn on_bright_purple(&self) -> BgColorDisplay<'_, BrightMagenta, Self>
fn on_bright_purple(&self) -> BgColorDisplay<'_, BrightMagenta, Self>
Source§fn bright_cyan(&self) -> FgColorDisplay<'_, BrightCyan, Self>
fn bright_cyan(&self) -> FgColorDisplay<'_, BrightCyan, Self>
Source§fn on_bright_cyan(&self) -> BgColorDisplay<'_, BrightCyan, Self>
fn on_bright_cyan(&self) -> BgColorDisplay<'_, BrightCyan, Self>
Source§fn bright_white(&self) -> FgColorDisplay<'_, BrightWhite, Self>
fn bright_white(&self) -> FgColorDisplay<'_, BrightWhite, Self>
Source§fn on_bright_white(&self) -> BgColorDisplay<'_, BrightWhite, Self>
fn on_bright_white(&self) -> BgColorDisplay<'_, BrightWhite, Self>
Source§fn bold(&self) -> BoldDisplay<'_, Self>
fn bold(&self) -> BoldDisplay<'_, Self>
Source§fn dimmed(&self) -> DimDisplay<'_, Self>
fn dimmed(&self) -> DimDisplay<'_, Self>
Source§fn italic(&self) -> ItalicDisplay<'_, Self>
fn italic(&self) -> ItalicDisplay<'_, Self>
Source§fn underline(&self) -> UnderlineDisplay<'_, Self>
fn underline(&self) -> UnderlineDisplay<'_, Self>
Source§fn blink(&self) -> BlinkDisplay<'_, Self>
fn blink(&self) -> BlinkDisplay<'_, Self>
Source§fn blink_fast(&self) -> BlinkFastDisplay<'_, Self>
fn blink_fast(&self) -> BlinkFastDisplay<'_, Self>
Source§fn reversed(&self) -> ReversedDisplay<'_, Self>
fn reversed(&self) -> ReversedDisplay<'_, Self>
Source§fn strikethrough(&self) -> StrikeThroughDisplay<'_, Self>
fn strikethrough(&self) -> StrikeThroughDisplay<'_, Self>
Source§fn color<Color>(&self, color: Color) -> FgDynColorDisplay<'_, Color, Self>where
Color: DynColor,
fn color<Color>(&self, color: Color) -> FgDynColorDisplay<'_, Color, Self>where
Color: DynColor,
OwoColorize::fg or
a color-specific method, such as OwoColorize::green, Read moreSource§fn on_color<Color>(&self, color: Color) -> BgDynColorDisplay<'_, Color, Self>where
Color: DynColor,
fn on_color<Color>(&self, color: Color) -> BgDynColorDisplay<'_, Color, Self>where
Color: DynColor,
OwoColorize::bg or
a color-specific method, such as OwoColorize::on_yellow, Read moreSource§fn fg_rgb<const R: u8, const G: u8, const B: u8>(
&self,
) -> FgColorDisplay<'_, CustomColor<R, G, B>, Self>
fn fg_rgb<const R: u8, const G: u8, const B: u8>( &self, ) -> FgColorDisplay<'_, CustomColor<R, G, B>, Self>
Source§fn bg_rgb<const R: u8, const G: u8, const B: u8>(
&self,
) -> BgColorDisplay<'_, CustomColor<R, G, B>, Self>
fn bg_rgb<const R: u8, const G: u8, const B: u8>( &self, ) -> BgColorDisplay<'_, CustomColor<R, G, B>, Self>
Source§fn truecolor(&self, r: u8, g: u8, b: u8) -> FgDynColorDisplay<'_, Rgb, Self>
fn truecolor(&self, r: u8, g: u8, b: u8) -> FgDynColorDisplay<'_, Rgb, Self>
Source§fn on_truecolor(&self, r: u8, g: u8, b: u8) -> BgDynColorDisplay<'_, Rgb, Self>
fn on_truecolor(&self, r: u8, g: u8, b: u8) -> BgDynColorDisplay<'_, Rgb, Self>
Source§impl<T> Pipe for Twhere
T: ?Sized,
impl<T> Pipe for Twhere
T: ?Sized,
Source§fn pipe<R>(self, func: impl FnOnce(Self) -> R) -> Rwhere
Self: Sized,
fn pipe<R>(self, func: impl FnOnce(Self) -> R) -> Rwhere
Self: Sized,
Source§fn pipe_ref<'a, R>(&'a self, func: impl FnOnce(&'a Self) -> R) -> Rwhere
R: 'a,
fn pipe_ref<'a, R>(&'a self, func: impl FnOnce(&'a Self) -> R) -> Rwhere
R: 'a,
self and passes that borrow into the pipe function. Read moreSource§fn pipe_ref_mut<'a, R>(&'a mut self, func: impl FnOnce(&'a mut Self) -> R) -> Rwhere
R: 'a,
fn pipe_ref_mut<'a, R>(&'a mut self, func: impl FnOnce(&'a mut Self) -> R) -> Rwhere
R: 'a,
self and passes that borrow into the pipe function. Read moreSource§fn pipe_borrow<'a, B, R>(&'a self, func: impl FnOnce(&'a B) -> R) -> R
fn pipe_borrow<'a, B, R>(&'a self, func: impl FnOnce(&'a B) -> R) -> R
Source§fn pipe_borrow_mut<'a, B, R>(
&'a mut self,
func: impl FnOnce(&'a mut B) -> R,
) -> R
fn pipe_borrow_mut<'a, B, R>( &'a mut self, func: impl FnOnce(&'a mut B) -> R, ) -> R
Source§fn pipe_as_ref<'a, U, R>(&'a self, func: impl FnOnce(&'a U) -> R) -> R
fn pipe_as_ref<'a, U, R>(&'a self, func: impl FnOnce(&'a U) -> R) -> R
self, then passes self.as_ref() into the pipe function.Source§fn pipe_as_mut<'a, U, R>(&'a mut self, func: impl FnOnce(&'a mut U) -> R) -> R
fn pipe_as_mut<'a, U, R>(&'a mut self, func: impl FnOnce(&'a mut U) -> R) -> R
self, then passes self.as_mut() into the pipe
function.Source§fn pipe_deref<'a, T, R>(&'a self, func: impl FnOnce(&'a T) -> R) -> R
fn pipe_deref<'a, T, R>(&'a self, func: impl FnOnce(&'a T) -> R) -> R
self, then passes self.deref() into the pipe function.Source§impl<T> Tap for T
impl<T> Tap for T
Source§fn tap_borrow<B>(self, func: impl FnOnce(&B)) -> Self
fn tap_borrow<B>(self, func: impl FnOnce(&B)) -> Self
Borrow<B> of a value. Read moreSource§fn tap_borrow_mut<B>(self, func: impl FnOnce(&mut B)) -> Self
fn tap_borrow_mut<B>(self, func: impl FnOnce(&mut B)) -> Self
BorrowMut<B> of a value. Read moreSource§fn tap_ref<R>(self, func: impl FnOnce(&R)) -> Self
fn tap_ref<R>(self, func: impl FnOnce(&R)) -> Self
AsRef<R> view of a value. Read moreSource§fn tap_ref_mut<R>(self, func: impl FnOnce(&mut R)) -> Self
fn tap_ref_mut<R>(self, func: impl FnOnce(&mut R)) -> Self
AsMut<R> view of a value. Read moreSource§fn tap_deref<T>(self, func: impl FnOnce(&T)) -> Self
fn tap_deref<T>(self, func: impl FnOnce(&T)) -> Self
Deref::Target of a value. Read moreSource§fn tap_deref_mut<T>(self, func: impl FnOnce(&mut T)) -> Self
fn tap_deref_mut<T>(self, func: impl FnOnce(&mut T)) -> Self
Deref::Target of a value. Read moreSource§fn tap_dbg(self, func: impl FnOnce(&Self)) -> Self
fn tap_dbg(self, func: impl FnOnce(&Self)) -> Self
.tap() only in debug builds, and is erased in release builds.Source§fn tap_mut_dbg(self, func: impl FnOnce(&mut Self)) -> Self
fn tap_mut_dbg(self, func: impl FnOnce(&mut Self)) -> Self
.tap_mut() only in debug builds, and is erased in release
builds.Source§fn tap_borrow_dbg<B>(self, func: impl FnOnce(&B)) -> Self
fn tap_borrow_dbg<B>(self, func: impl FnOnce(&B)) -> Self
.tap_borrow() only in debug builds, and is erased in release
builds.Source§fn tap_borrow_mut_dbg<B>(self, func: impl FnOnce(&mut B)) -> Self
fn tap_borrow_mut_dbg<B>(self, func: impl FnOnce(&mut B)) -> Self
.tap_borrow_mut() only in debug builds, and is erased in release
builds.Source§fn tap_ref_dbg<R>(self, func: impl FnOnce(&R)) -> Self
fn tap_ref_dbg<R>(self, func: impl FnOnce(&R)) -> Self
.tap_ref() only in debug builds, and is erased in release
builds.Source§fn tap_ref_mut_dbg<R>(self, func: impl FnOnce(&mut R)) -> Self
fn tap_ref_mut_dbg<R>(self, func: impl FnOnce(&mut R)) -> Self
.tap_ref_mut() only in debug builds, and is erased in release
builds.Source§fn tap_deref_dbg<T>(self, func: impl FnOnce(&T)) -> Self
fn tap_deref_dbg<T>(self, func: impl FnOnce(&T)) -> Self
.tap_deref() only in debug builds, and is erased in release
builds.