# Parameters Specification
Specify *where to get the value* for each item's input.
The value may not necessarily exist until the flow is executed.
```dot process
digraph {
graph [
margin = 0.0
penwidth = 0
nodesep = 0.0
ranksep = 0.02
bgcolor = "transparent"
fontname = "helvetica"
fontcolor = "#7f7f7f"
rankdir = LR
// splines = curved
]
node [
fontcolor = "#111111"
fontname = "monospace"
fontsize = 12
shape = "circle"
style = "filled"
width = 0.3
height = 0.3
margin = 0.04
color = "#9999aa"
fillcolor = "#ddddf5"
]
edge [
arrowsize = 0.7
color = "#7f7f7f"
fontcolor = "#7f7f7f"
]
subgraph cluster_a {
a [label = <<b>a</b>>]
a_text [shape="plain" style="" fontcolor="#7f7f7f" label = <<table border="0" cellborder="0" cellpadding="0"><tr>
<td><font point-size="15">📥</font></td>
<td balign="left">file<br/>download</td>
</tr></table>>]
subgraph cluster_a_params {
a_params_src [
label = "src"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
a_params_dest [
label = "dest"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
a_state [
label = < .. <br align="left"/>>
margin = 0.05
fontsize = 8
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffffaa"
color = "#667722"
]
}
a_params_src -> a_state [style = invis]
a_params_dest -> a_state [style = invis]
a -> a_state [style = invis]
}
subgraph cluster_b {
b [label = <<b>b</b>>]
b_text [shape="plain" style="" fontcolor="#7f7f7f" label = <<table border="0" cellborder="0" cellpadding="0"><tr>
<td><font point-size="15">🪣</font></td>
<td balign="left">s3<br/>bucket</td>
</tr></table>>]
subgraph cluster_b_params {
b_params_name [
label = "name"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
b_state [
label = <<b>S3BucketState</b> <br align="left"/> name<br align="left"/>>
margin = 0.05
fontsize = 8
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffffaa"
color = "#667722"
]
}
b_params_name -> b_state [style = invis]
b -> b_state [style = invis]
}
subgraph cluster_c {
c [label = <<b>c</b>>]
c_text [shape="plain" style="" fontcolor="#7f7f7f" label = <<table border="0" cellborder="0" cellpadding="0"><tr>
<td><font point-size="15">📤</font></td>
<td balign="left">s3<br/>object</td>
</tr></table>>]
subgraph cluster_c_params {
c_params_file_path [
label = "file_path"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
c_params_bucket_name [
label = "bucket_name"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
c_params_object_key [
label = "object_key"
margin = 0.0
fontsize = 8
width = 0.78
height = 0.19
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffaaff"
color = "#773377"
]
c_state [
label = < .. <br align="left"/>>
margin = 0.05
fontsize = 8
shape = "rectangle"
style = "filled,rounded"
fillcolor = "#ffffaa"
color = "#667722"
]
}
c_params_file_path -> c_state [style = invis]
c_params_bucket_name -> c_state [style = invis]
c_params_object_key -> c_state [style = invis]
c -> c_state [style = invis]
}
a -> b [minlen = 9, weight = 5]
b -> c [minlen = 9, weight = 5]
subgraph params {
label = "Pre-execution\nknown values"
cluster = false
node [
shape = none
fontsize = 8
margin = 0.05
height = 0.1
style = ""
]
edge [
color = "#4455ff"
arrowhead = "vee"
style = dashed
]
web_app_url;
web_app_path;
bucket_name;
object_key;
web_app_url -> a_params_src [constraint = true]
web_app_path -> a_params_dest [constraint = true]
{
edge [
color = "#cc7744"
]
bucket_name -> b_params_name [constraint = true, minlen = 10]
}
{
edge [
color = "#449988"
]
a_state -> c_params_file_path [constraint = false, style = invis]
b_state -> c_params_bucket_name [constraint = true]
}
web_app_path -> c_params_file_path [constraint = true, color = "#44dd77", minlen = 19]
object_key -> c_params_object_key [constraint = true, color = "#44dd77", minlen = 19]
}
}
```
```rust ,ignore
let app_download_params = FileDownloadParams::<WebApp> {
src: Url::parse("https://example.com/web_app.tar")?,
dest: PathBuf::from("/tmp/path/to/web_app.tar"),
marker: PhantomData,
};
let s3_bucket_params = S3BucketParams::<WebApp>::new(bucket_name);
let s3_object_params = S3ObjectParams::<WebApp> {
file_path: PathBuf::from("/tmp/path/to/web_app.tar"),
object_key: String::from("web_app.tar"),
bucket_name: !?, /* Somehow get the bucket name from `b` */
};
```
## Deferred Values
```rust ,ignore
// examples/envman/src/flows/app_upload_flow.rs
let s3_object_params_spec = S3ObjectParams::<WebApp>::field_wise_spec()
.with_file_path(PathBuf::from("/tmp/path/to/web_app.tar"))
.with_object_key(String::from("web_app.tar"))
.with_bucket_name_from_map(|s3_bucket_state: &S3BucketState| {
match s3_bucket_state {
S3BucketState::None => None,
S3BucketState::Some {
name,
creation_date: _,
} => Some(name.clone()), // type safe!
}
})
.build();
#
# let file_download_params_spec = file_download_params.into();
# let server_instance_params_spec = server_instance_params.into();
```
