Generated values reference

All types are in the Cratis.Concepts namespace of Cratis.Fundamentals.

Contracts

Type	Member	Meaning
`IGeneratable<TSelf>` where `TSelf : IGeneratable<TSelf>`	`static abstract TSelf New()`	Creates a value with the type’s own strategy
`IGeneratableInContext<TSelf>` where `TSelf : IGeneratableInContext<TSelf>`	`static abstract TSelf New(GenerationContext context)`	Creates a value from the operation’s captured time and tenant

If a type implements both, callers use the context form. Neither interface dispatches to the other.

public readonly record struct GenerationContext(DateTimeOffset Now, string Tenant)

Member	Value
`Now`	The time the operation was received
`Tenant`	A portable tenant identifier string
`const string DefaultTenant`	`"00000000-0000-0000-0000-000000000000"`

public static partial class GenerateValue. Every method uses a cryptographically secure generator.

Signature	Output shape	Random bits	Time-ordered	Limits and exceptions
`Guid Uuid()`	RFC 9562 version 4, RFC variant	122	No	None
`Guid UuidV7()`	RFC 9562 version 7 using the current UTC time	74	Yes	None
`Guid UuidV7(GenerationContext context)`	Version 7 using `context.Now`	74	Yes	`MissingGenerationTime`, `GenerationTimeBeforeUnixEpoch`
`string Ulid()`	26 uppercase Crockford base32 characters; first character `0` to `7`	80	Yes	None
`string Ulid(GenerationContext context)`	Same, using `context.Now`	80	Yes	`MissingGenerationTime`, `GenerationTimeBeforeUnixEpoch`
`string TypeId(string prefix)`	`prefix` + `_` + 26 lowercase Crockford characters; only the suffix for an empty prefix	74	Yes	`InvalidTypeIdPrefix`
`string TypeId(string prefix, GenerationContext context)`	Same, using `context.Now`	74	Yes	`InvalidTypeIdPrefix`, `MissingGenerationTime`, `GenerationTimeBeforeUnixEpoch`
`string NanoId(int size = 21, string? alphabet = null)`	`size` characters drawn uniformly from the alphabet	`size × log₂(alphabet length)`	No	`InvalidNanoIdSize`, `InvalidNanoIdAlphabet`
`string Bytes(int count, ValueEncoding encoding = ValueEncoding.Base64Url)`	Encoded random bytes, no padding	`8 × count`	No	`InvalidByteCount`, `UnknownValueEncoding`

Argument limits:

TypeID prefix: empty, or 1 to 63 lowercase letters (a–z) and underscores, starting and ending with a letter. A null or invalid prefix throws InvalidTypeIdPrefix.
NanoID size: 1 to 256. The default is 21.
NanoID alphabet: 2 to 256 distinct printable ASCII characters (0x20 to 0x7E). Null selects the default alphabet ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789_-, 64 characters, so the default 21 characters carry 126 bits.
Bytes count: 1 to 512.
Context time: Now equal to default throws MissingGenerationTime; a Now before 1970-01-01T00:00:00Z throws GenerationTimeBeforeUnixEpoch.

Member	Value	Output of `Bytes`
`Base64Url`	0	RFC 4648 URL-safe base64 without padding; 32 bytes give 43 characters
`Hex`	1	Lowercase hexadecimal; 32 bytes give 64 characters
`Base32`	2	RFC 4648 uppercase `A`–`Z`, `2`–`7` without padding; 20 bytes give 32 characters

An undefined enum value throws UnknownValueEncoding.

Exception	Thrown when
`MissingGenerationTime`	A context overload receives a `default` `Now`
`GenerationTimeBeforeUnixEpoch`	A context overload receives a `Now` before the Unix epoch
`InvalidTypeIdPrefix`	The TypeID prefix is null or breaks the prefix rule
`InvalidNanoIdSize`	The size is outside 1 to 256
`InvalidNanoIdAlphabet`	The alphabet is outside 2 to 256 characters, not distinct, or not printable ASCII
`InvalidByteCount`	The count is outside 1 to 512
`UnknownValueEncoding`	The encoding is not a defined `ValueEncoding`

ULID and TypeID encode 128 bits as 26 base32 characters. 128 is not a multiple of 5, so two zero bits are added at the start, and the first character is 0 to 7.
A ULID is 48 bits of big-endian Unix milliseconds followed by 80 random bits. Its alphabet is 0123456789ABCDEFGHJKMNPQRSTVWXYZ.
A TypeID suffix is the 16 big-endian bytes of a UUID v7 in the lowercase alphabet 0123456789abcdefghjkmnpqrstvwxyz.
The first 10 characters of either encoding carry the 48-bit timestamp.

Runtime	Implementation
.NET 9 and later	Delegates to `Guid.CreateVersion7` with the supplied time
.NET 8	Built-in polyfill: six timestamp bytes, version 7 and RFC variant bits set, 74 bits from `RandomNumberGenerator`

Values from both are time-ordered but not monotonic within one millisecond. Clock adjustments can move timestamps backward.

Every strategy uses RandomNumberGenerator. NanoID chooses characters with RandomNumberGenerator.GetItems<char>, so each character is uniform.
There is no seeded Random, injectable generator, seed configuration or within-millisecond counter.
The helpers and the static interface calls use no reflection or dynamic code and are safe for Native AOT and trimming.
Targets: .NET 8, 9 and 10.