Composite types
Options
An option is convenient when a variable may or may not have a value of a given type.
Declare
some andnone are the 2 operators to build an option value.1
variable receiver : option<address> = none // to be set later ...
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variable message : option<string> = some("there is a message")
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Test
issome and isnone are the 2 operators to test whether an option value is none or is some.1
entry testopt (a : option<int>) {
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requires {
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r1 : issome(a);
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}
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failif {
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f1 : isnone(a);
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}
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effect {
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...
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}
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}
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Get
opt_get is the operator to extract the value from a some option value. It fails if the value is none.1
effect {
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var a = some("a string");
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if issome(a) then (
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if opt_get(a) = "a string" then transfer 1tz to coder;
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);
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}
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Tuples
Tuples are like vectors of values. For example, the following declares a tuple of three values, an integer on the first dimension, a string on the second and a bytes on the third:
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variable t : int * string * bytes = (2020, "is the year of", 0x050100000009617263686574797065)
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The tuple type is built with
* and the tuple value with (,) syntax.The
[ ] operator is used to project the tuple to one specific dimension:1
effect {
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var t = (2020, "is the year of", 0x050100000009617263686574797065);
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var y = t[0]; /* 2020 */
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var s = t[1]; /* "is the year of" */
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var b = t[2]; /* 0x050100000009617263686574797065 */
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}
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Projection fails if the dimension index is invalid.
The dimension index must be a straightforward literal of integer. It does not support any expression, even an expression that would reduce to an integer value. For example, the following does not compile:
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var y = t[1-1]; /* does NOT compile! */
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Records
A record is a list of named values. For example, the following declares a record of two values:
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record geoloc {
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longitude : rational;
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latitude : rational;
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}
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It is possible to read and assign values to the fields of a record:
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var r : geoloc = { /* Eiffel tower's location */
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longitude = 48.8583701;
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latitude = 2.2944813
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};
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var lo = r.longitude; /* lo = 48.8583701 */
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var la = r.latitude; /* la = 2.2944813 */
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/* let's go to another Eiffel's construction! */
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r.longitude := 40.6892494;
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r.latitude := 74.04;
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Enums
An enum is a union type, that is a value taken from a list of possible values. For example the the following enum defines 3 possible colors:
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enum Color =
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| Red
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| Green
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| Blue
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You can then create a value by using one of the three possible values:
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var c = Red;
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You can test the value with
= and <> comparison operators. You can also check for any of the possible values with match ... with end instruction:1
match c with
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| Red -> ...
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| Green -> ...
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| Blue -> ...
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end;
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Note that this instruction fails to compile if one case is omitted.
An enum type may be parameterised by other types. For example :
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enum Color =
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| RGB <nat * nat * nat>
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| YUV <nat * nat * nat>
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| CMY <nat * nat * nat>
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You can then deconstruct a
color value the following way:1
match c with
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| RGB (red, green, blue) -> ...
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| YUV (lum, chrom1, chrom2) -> ...
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| CMY (cyan, magenta, yellow) ->
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end
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Last modified 2mo ago