expect-actual

expect-actual is a skill for Claude Code, Codex from TalissonVitorino/kmp-ios-skills. It costs 73 tokens per session (2,911 once invoked), scanned A, original, MIT.

A guide to Kotlin's expect/actual pattern for declaring one shared API and supplying platform-specific implementations. Kotlin Multiplatform uses this pattern when shared code needs different Android and iOS behavior.

In plain words
What is it for?
Use it for small platform services such as device information and other thin platform-specific adapters in a multiplatform project.
Why use it?
It reduces duplicated calling code while keeping platform details in the appropriate source set. The guide also explains when a shared interface and factory are a better boundary than an expect/actual class.

Skill for Claude CodeCodex

Written for no agent in particular: nothing here depends on one.

Good fit Use it for small platform services such as device information and other thin platform-specific adapters in a multiplatform project.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/talissonvitorino/kmp-ios-skills/expect-actual
Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

Any agent
npx skills add TalissonVitorino/kmp-ios-skills --skill expect-actual
Clone the repo
git clone --depth 1 https://github.com/TalissonVitorino/kmp-ios-skills

Made for: Claude Code, Codex.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

agentmods badge for expect-actual

README.md
[![agentmods](https://agentmods.dev/badge/skills/talissonvitorino/kmp-ios-skills/expect-actual/github.svg)](https://agentmods.dev/skills/talissonvitorino/kmp-ios-skills/expect-actual)
Your own site
<a href="https://agentmods.dev/skills/talissonvitorino/kmp-ios-skills/expect-actual"><img src="https://agentmods.dev/badge/skills/talissonvitorino/kmp-ios-skills/expect-actual/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

agentmods 80×15 button for expect-actual

Your own site · 80×15
<a href="https://agentmods.dev/skills/talissonvitorino/kmp-ios-skills/expect-actual"><img src="https://agentmods.dev/badge/skills/talissonvitorino/kmp-ios-skills/expect-actual.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 73 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 2,911 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe. Third-party audits
  • NVIDIA SkillSpector warn 7 Sept 2026
SkillSpector: 6 findings, up to high

These are SkillSpector’s own severities. On a checked sample its high-severity flags on skills were ~96% false positives — a documented command, a public API, a “never do X” rule — so we show them as a caution to read, not a verdict. Why →

  • high Privilege Escalation · line 230
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 232
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 232
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 235
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 239
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
  • high Privilege Escalation · line 243
    Code accesses credential files (SSH keys, AWS credentials, etc.). This could indicate credential theft attempts.
    Fix: Remove references to credential paths. Use environment variables or secrets managers. For docs, use placeholder paths (e.g., /path/to/config). Never load .env or token files in production code paths.
How audits are shown
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5.1 $0.00073 $0.02911
Opus 5 $0.00036 $0.01456
Sonnet 5 $0.00015 $0.00582
Haiku 4.5 $0.00007 $0.00291

Measured 9d ago against content hash f3ca3a59bbf7, method: parsed. Prices are Anthropic first-party input rates as of 2026-09-12, from the pricing page.

Security

Grade A, and why

expect-actual scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 9d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

kmp/expect-actual/SKILL.md · 395 lines

How it starts

The opening of the file, as written. The whole thing — 395 lines — stays where its author put it; the contents beside it link to each section on GitHub.

expect/actual Pattern for KMP

The expect/actual declaration is Kotlin's mechanism for writing platform-specific implementations while maintaining a shared API surface.

Core Concept

// shared/commonMain/kotlin/Platform.kt
expect class Platform() {
    val name: String
}

// shared/androidMain/kotlin/Platform.android.kt
actual class Platform {
    actual val name: String = "Android ${Build.VERSION.SDK_INT}"
}

// shared/iosMain/kotlin/Platform.ios.kt
actual class Platform {
    actual val name: String = "iOS ${UIDevice.currentDevice.systemVersion}"
}

Beta note: expect/actual classes (and objects/interfaces/enums/actual typealiases) are still Beta in Kotlin 2.x — the compiler warns unless you add freeCompilerArgs.add("-Xexpect-actual-classes"). Expect functions and properties are stable. For anything beyond a thin platform shim, prefer a common interface + expect factory function; see android-skills:kmp-boundaries for choosing the boundary shape.

Common Patterns

1. Platform Information

// commonMain — a singleton, so `expect object`; named PlatformInfo because
// the `expect class Platform()` above already occupies that name in the package
expect object PlatformInfo {
    val name: String
    val version: String
    val isDebug: Boolean
}

// androidMain
actual object PlatformInfo {
    actual val name: String = "Android"
    actual val version: String = "${Build.VERSION.SDK_INT}"
    // BuildConfig needs buildFeatures.buildConfig = true (off by default in AGP 8+;
    // not generated at all by the AGP KMP library plugin)
    actual val isDebug: Boolean = BuildConfig.DEBUG
}

// iosMain
// kotlin.native.Platform is annotated @ExperimentalNativeApi (whole object)
@OptIn(kotlin.experimental.ExperimentalNativeApi::class)
actual object PlatformInfo {
    actual val name: String = "iOS"
    actual val version: String = UIDevice.currentDevice.systemVersion
    actual val isDebug: Boolean = kotlin.native.Platform.isDebugBinary
}

Read the full file on GitHub · 395 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 9d ago First seen · 395 lines · 73 tokens per session scan A f3ca3a59bbf7

Subscribe to this mod's changes

expect-actual is a skill published in the GitHub repository TalissonVitorino/kmp-ios-skills (12 stars, last pushed 18d ago), licensed MIT. It adds 73 tokens to every session and 2,911 once invoked, about $0.0004 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-09-03.

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